i have a 97 silverado half ton and its started to do some pretty funny things. after i drive for about 10-15 miles the check engine light will come on and the truck will start to drop hard into all the gears. but if i shut it off and let it sit for a little while the engine light goes off and its fine for another 10-15 miles. Another thing is that when im going down the road the whole truck will start to shake and stutter like the tranny is slipping. it shakes so bad the it spills what ever is in the cup holder but if i let off the gas and get on it again it goes away. i dont even know where to start. i have heard its everything from the drive shaft to the drum , the u joints, the tranny just needs to be rebuilt, maybe the transfer case is shot, even that the battery isn't putting out enough voltage. any help would be greatly appreciated

well, you start at the very beginning:

drag your truck to nearest autozone/napa/petshop boys/schucks, and have error codes scanned. have no doubt with such rude attitude towards your coffe cups there will be at least several of them.

Another thing to check is the condition of the fluid,if it looks motor oil and smells bad,burned up clutches.If it is pink in clor,that is good.The transfer cases are known for breaking snap rings in the tailshaft area.Remove the drive shaft,pull the cover held in with 4 15mm headed bolts.Look for pieces of a broken snap ring in the cover.