1994-1997 SR has the locker from what I hear. But, those years have the 3.5L?
My understanding is that the 3.5 DOHC came in the SRs from 1994-1997, after that the 3.5 SOHC was used. I may have the years wrong but I'm sure someone will correct me if they are.
The engine will run on regular unleaded - premium is only recommended, not required. I usually run mid-grade around town but can definitely feel the difference in power when I run a tank of premium through it. I get about 1/2 mpg better mileage with premium also, so it's almost worth it.
The 3.5 DOHC has a known issue with the variable intake butterfly valves working themselves loose & getting swallowed by the engine. The butterfly shaft itself is prone to wearing out the bushings and creating a vacuum leak - it's probably this looseness that allows vibrations to work the butterfly screws loose. Some people have taken the lower intake plenum off, removed the shaft and plugged the holes rather than spend the money to replace it when it goes bad, and usually report no noticeable difference in power. In my opinion that's removing a piece of an engineered system that Mitsubishi spent a lot of time designing. If there wasn't an advantage to it, I'm pretty sure they wouldn't have put it on the engine in the first place. It's kind of like removing your fuel injection system because you've got a couple of bad injectors, and replacing it with a carburetor because it's cheaper & easier to work on.
Anyway, if you're looking at a 3.5 DOHC make sure you check for any play in that shaft, along with verifying the age of the timing belt. The timing belt is do-able but challenging for an average home mechanic due to the complexity of the engine. If the vehicle you're looking at needs it done make sure you include that in your negotiations because it's not a quick & easy job.
The 3.5 DOHC is a complicated engine, but is very strong & reliable. Mine hasn't needed anything except maintenance under the hood for over 50k miles now. My oil pressure gauge has stopped working but I'm sure that's due to the salt water drowning the truck endured about a year ago.
Oh yeah - almost forgot, make sure you check to see if the crankshaft pulley bolt has been replaced with the updated version. Mitsubishi updated the design and the torque setting for it - several people here can attest to the issues that occur if it's not updated. <img src="/forums/images/graemlins/frown.gif" alt="" /> Search this forum for info on it - it's been covered numerous times with pictures and part numbers.
