01 denali wont cooperate!

[tswore]

Hey all, Im looking for some brilliance here. I have an 01 denali with the 6.0 in it that is givin me some fits. My wife called me the other day as she left work and said there was something wrong withe the transmission, it was all she could do to get the rig up to speed. She brought it by my work so I could look at it, and sure enough it seemed like the trans was effed up. The next day i tried to move it, and it ran good for about 2 minutes, then the same thing, seems like the trans was bad. So as i was diagnosing it it would run fine in park, but as soon as I put it in gear it would die. if I revved it then dropped it in gear it would move a little. By now I had ruled out the trans being a problem. Now (3 weeks later just letting it sit) when I start it it will run for like 5 seconds then die. It will do that 3 or 4 times then not start again for a few hours. I have swapped the MAF sensor with the one on my truck-no help, swapped the crank position sensor-no help, new o2 sensors on the upflow-no help (and ouch! $140) and unplugged the downflow ones-no help either. I am kinda at a loss here, dont know what else to try. I am about ready to take it to a mechanic to have them check it out, but dont really want to. If anybody has any input, please fire away, I am all ears!