Well, I've been WAY out of town for awhile. I've gotten most of the engine replacement issues worked out. Here's what I've got left. Let me start off by saying that the tires are freshly rotated and balanced, so this is likely n ot the issue. Also, exhaust is all intact, with no holes.
I have a loud low hum/vibration during acceleration starting around 60MPH..it fades, and shows up again around 75MPh. I can reproduce the noise in park by slowly revving the engine to around 2250rpm and 3250rpm.
However, if I am at the 60mph or 75mph range when the noise is happening, I can put the truck in Neutral and rev all I want, it does not affect the noise. Finally, the noise/vibration seems at it's worst during DE-celeration around that magical 60mph area, and is most noticable after you've been driving a while.
So, I've spent over 6000 getting the engine running right...please tell me my torque converter isn't going out or something.
Ideas? Where should I start looking?
This problem was not there before the engine was replaced; trans. fluid changed to Amsoil, and trans/diff/x-fer case drain filled.

Thanks again.
Shawn

Any chance it could be coming from the steering column? If not, can you narrow-down from what area the noise seems to be coming? Since you can duplicate it while standing still, might want to get an assistant and have them rev the engine to reproduce the noise while you listen here and there.

I see in your profile that you have a '95 Montero SR. I'm not familiar with the transmission in the '95 - but a word about the earlier models:

I recently bought a rebuilt torque converter for a '91 A/T which has a lockup torque converter. The installation instructions included a caution to replace the torque converter bolts with new ones since the bolts stretch when torqued. In the earlier KM148 non-lockup versions the bolt stretch may or may not not be an issue, but the lack of internal clearance in the lockup version definitely causes torque converter damage. DougB and I have measured the length of a new torque converter bolt and compared it to a used bolt. We both found the caution wrt to bolt stretch to be correct. I'm not sure the bolt issue applies to your torque converter.... nor am I sure if it applies to OE converters that have not been remanufactured.

All that said, I don't think your problem is in the transmission. Since the vibration is evident in PARK at 2250/3250, you can eliminate the drive shaft as a suspect. Since it happens at 60/75 AND when revved in PARK - yet isn't affected by a change in engine rpms while moving, I suspect the problem may be related to air movement. I'd suggest a thorough check of everything around the grille, behind the engine cooling fan and all of the air intake system. I'd also check the heat shields on the exhaust manifolds - even the catalytic converter.

Frank

Here's the latest scoop. Thanks for the suggestions thus far.
I think though the vibrations are similar, it seems the vibration at 75+ might just be normal wear/tear. It's not really that bad, and shows up all the time at that speed.
However, I was not hearing the noise or feeling any vibration after leaving work today. No noise at rev in Park, and nothing at 60. UNTIL....I drove it around a while. Then the noise/vibration were both back. So, the truck needs to be "warmed -up" pretty good to reproduce the problem. When I returned from driving around, I tried revving the engine, and noticed it is a quite loud, low-pitched hum. It seems to be coming from right around the firewall area, but it's really hard to tell.
Would the torque converter vibrate in park?
I am really lost considering the fact that I need to drive around awhile before the noise shows up.

Normal wear and tear doesn't excuse vibrations - vibrations are an indication that something isn't right.

Which side of the truck is loudest? If it's the passenger side, I'd at least check the catalytic converter heat shield.... and I'd check the exhaust manifold heat shields - both sides.

Frank

Would those heat shields not make noise until really warmed up?

I don't know..... but like most things - you won't find the problem until you start pokin' 'round and eliminating the easy and cheap questions.

Frank

Ok, you have eliminated driveline vibration, as the problem can be duplicated when the vehicle is parked. Now remove all the accessory drive belts and rev the engine to the range of the vibration. If the vibration is still there, you have eliminated all the driven components including the fan. If the vibration is gone, check the driven components.
Conner

Conner, the reason I thought it might be wind/air movement related and not driven parts related is because when driving and the noise shows up, putting it in Neutral and revving the engine has no effect.... perhaps it's load related.... weird, though. I agree that removing the belts might show something though... good idea.

Frank

Frank: I try to eliminate as much as possible when checking engine vibration problems and belt removal is usually the first step. You have a good point concerning the reving in neutral it when moving. Now i am starting to believe that we may have a worn or misadjusted roll-stopper. I have seen these things set up all kinds of weird vibrations and noises at different rpms. I believe the engine was replaced not long ago. Worth a look.
Conner