I'm new here, but not new to auto repair

96' - Blazer - 4X4 - 4.3L - 4L60-E

I just bought this blazer about a week ago and have been going through it fixing it's many problems, but the latest has me stumped.

I'm having upshift and downshift problems. it seems to shift late into 3rd like really really late 2900rpm at 1/4-1/2 throttle. first thought is it's slipping, but no. I back probed the 2/3 shift solenoid and drove with it and found that the VCM is not letting off the 2/3 solenoid until 2900rpm (3rd gear 1-2 and 2-3 should be off). Tried a new VCM some luck it's upshifting earlier more like 2200rpm. On to the second symptom. WOT from a stop 1-2 fine but NO upshift to 3rd it just goes to rev limit and screams. Again, I back probed and found the VCM is not letting off the 2-3 solenoid (also confirmed by scan-tool) . If I let off the throttle to about 3/4 It upshifts and drives fine. and now here's the part that's really pissing me off, while cruising at any speed if you go above 3/4 throttle it immediately down shifts to 2nd. I have confirmed that this is what the VCM is commanding the trans to do by way of scan tool and backprobing. It dosen't make sense that the VCM would command 2nd gear while at 65mph (duh)

I'm thinking about swapping the VSS just for S&G's the spedo is correct so I don't think that's the issue.

Any ideas?

Thanks for your time

 

TPS maybe? The PCM doesn't recognise when the throttle is at or near to WOT & it won't make the right adjustments for the 4L60E - E being Electronic as we all know.

Reminds me of a vacuum secondary issue, but not in this case.