so my buddy has a 2000 chevy silverado 4x4 with a 5.3L v8 and 4l60e tranny. The tranny is new with only 8000 miles on it and last night he lost 3rd gear and over drive. Reverse, 1st and 2nd are fine. Tranny fluid looks brand new yet and doesn't smell burnt. He's been having some engine problems lately. so my question, could an engine related problem cause it to go into limp mode?

the symptoms the truck has,

hard starting. it doesn't do it all the time but sometimes you have to crank on it to get it to start. also when started it runs rough and almost kills unless you feather the gas but its fine after you feather it. Also sometimes going down the highway it doesn't want to acelerate and feels like its missing.

any idea's?

bring it to autozone and have them see what trouble codes the computer is throwing. Then go from there. Just dont buy all the useless shit autozone will try to sell you after the free diagnostic check is done.

Just a guess, but I suggest that there may be a problem with the MAP sensor, BARO sensor, or there's a manifold vacuum leak somewhere. The OBDII readout (using the above suggested AutoZone loaner tool) may help to verify that.