i have done a search but i couldn't find anyone with the same problem i'm having. i wanna see if anyone has had similar problems with their 4wd as i have. my 4wd will only engage when the motor hasn't warmed up to normal temp. if i keep it in 4wd until the motor warms up to normal temp, it will stay in 4wd. but as soon as i put it back in 2wd and try to go back to 4wd, it won't. that's only when the motor is warm though. when ever the motor is still cold, it switches in and out of 4wd just normal. just having problems with it when motor reaches normal temp. any help would be appreciated.

It sounds like you have a vacum leak the automatic hubs need vacum to operate. I would check out all your vacum hoses. My guess as to why that it wouldn't engauge is that when you are idling at a lower rpm after warm up the vacum has dropped off to a point where their isn't enough to engauge the system. You didn't say if you have a stick or auto but either way you could try holding the rpms at like 2,000 in neutral and see if it will go in then. If it does then more than likely its a vacum leak somewhere. If not then more info would be nice miles, last change of fluids, does it engauge while driving below 45, etc....

I explained a bit how 4wd is engaged in these trucks in this thread:
http://www.4x4wire.com/forums/showflat.php?Cat=&Number=935608

I can't see how engine temperature would have any effect unless maybe there was a loose connection somewhere that opened up when heated...?

Its been a while since I read all the engagement literature but my thinking was that if he was sitting idling since your idle drops off after the truck warms up say from 1500-1100 cold to 500 warm depending on the outside temp that the vacuum would drop off. So if there was a leak it would be enough to cause the system not to engauge at idle. Then again I could be totally off in left field.

The truck actually has more manifold vacuum avaible at idle than higher RPMs.