Chevy venture stumbles upon acceleration

My Venture LS is stumbling upon accleration. It starts to occur around 35 mph and then continues with occasional smooth sailing. No rough idle and no stumble when coasting. I had the spark plugs and wires replaced at the dealer today and it did nothing. Fuel trim is fine, LT runs from 0 to - 5 . I replaced the MAF sensor a few months ago and all other sensors test OK on the scanner. Any ideas?

Also, I took my car to the dealership to have the plugs and wires replaced and they used the after market wires named Xact. I have never been to a dealer where they used aftermarket parts. I thought that they were required by GM to use their parts? Anyone have any experience with these wires?

Update: Took it back to the dealership and was told they made a few adjustments and everything was fine. Problem solved car ran great until about 1 hour after leaving the dealership. The check engine light came on with DTC 1860, 0758, 755 and 740. I guess this means my Torque converter Solenoid is shot. That was probably the stumbling that I felt. Anyone with any experience with this?

Did they change the plugs and wires, because you told them to, or was this their solution?......whenever you have a driveability problem, it's always a good idea to drive the car with a tech in the passenger seat and scan tool hooked up, while you recreate the problem for him....the scan tool will tell him if it's a trans or engine problem....

No, the plugs had 90000 miles on them, and I had not had any transmission problems. I just assumed that it was the plugs and wires . I was afraid that the dealership would try to rip me off. The plugs and wires needed to be replaced anyway, so I thought that I might as well give it a shot
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Turned out to be a short in the internal transmission harness. Dealer ship wants $850.00 to replace. My mechanic wants $1200.00 to put in a used tranny (61,000 miles). I hoped that it would be something simple, but sonehow that never seems to be the case..oh well, used tranny it is.

WTF? 850 to fix or 1200 to replace with UNKNOWN USED transmission, are you crazy? Fix what you have.... unless you have severly beat on it or something and the internals are trash..... while they are in it replacing the harness they should replace the filter (I would assume) and they will refill with new fluid...... should be better than a J/Y trans even if it has 30k less miles and you save 350 bucks....

The Tranny I have now has 250,000 miles on it and seems to me ok. However the cost to fix the wiring harness is $850.00 and the cost to replace with the 60,000 mile tranny is $1200.00. I think I'll roll the dice with the 60,000 mile tranny for an extra $350.00

My bad, thought you had 90k, guess that were the plugs, if trans is that high of mileage, have them flush the trans cooler lines and drop that 60k unit in...........

Thanks, I originally forgot to list the mileage on the tranny. I've been looking on the internet and it appears the venture tranny's are pretty reliable except for the solenoid issues.