I have a 2001 Chevy Venture. When I step on the gas the engine will rev, but power through the transmission is sluggish. When I disconnected the battery it reset the check engine light. When I hooked the battery back up and took a test drive I stepped on the gas the engine revved high but I wasn't getting any pep, just sluggish acceleration. Then the check engine light started flashing and when I depressed the gas pedal to cruise the check engine light stopped flashing. After about 70 miles the check engine light came back on to stay. I stopped by an autozone and they put the scanner on it and it showed problems with the EGR valve and aft O2 sensor. Another thing I find odd is that I am getting a high pitched whining only when driving. When I stop and park and rev the engine I don't here the whine. Also when I take off sometimes the serpertine belt squeals and after I cut the engine off for sometime and then restart the starting is sluggish and after it starts my door locks and CD player act as if the battery cable was rehooked up. Sometimes when i step on the gas from a stop the engine will rev and then as if someone cut on a switch the van will accelerate like it used to. The van has 253,000 miles so I can assume there is a lot wrong with it.

 

Im no mechanic but i dont think your EGR or "exhaust gas recirculation" valve has anything to do with trans problems.... sounds to me like you have a number of issues.... My 01 venture has a code of P0420 which is an emissions code so my check engine light stays on all the time also.... could it be the front o2 sensor or the rear? im too lazy to fix it right this second, but it has nothing to do with the way my trans shifts or drives.... nor do i think ur serpentine belt has anything to do with it either.....
Have you noticed leakage of ur trans fluid or any fluid for that matter under ur van.... with that many miles im sure it does... Have you ever changed the tranny fluid? I would look at the drive train rather than the engine.
but lke i said im just a "DIY" guy so im not completely sure i could be wrong.