1993 GMC Truck Overdrive problems

Tiny
BRI4017
  • MEMBER
  • 1993 GMC TRUCK
  • V8
  • 4WD
  • AUTOMATIC
  • 73,000 MILES
My truck will shift through all gears fine until I get on the highway and it shift down into 3rd to pass. After it shifts down it won't go back to overdrive at all not even if I stop. I have to turn the truck off to reset it. I have 36x14.5 inch tires on my 93 2500 sierra and installed a jet-accu speed chip to calibrate the speedometer and shifting. It help a little with the shifting. I feel like the rpms are higher than they should be even when it is in OD. Other gmc's rpm's are about 2000 at 65mph and mine is at 2500. Do you think it is just my tires or my transmission?
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Monday, August 23rd, 2010 AT 4:10 PM

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Tiny
BLUELIGHTNIN6
  • EXPERT
Hello and thanks for donating

I would definitely swap out the aftermarket wheels/tires to the OEM size first to see if this helps. That would be the easiest test. If it doesn't change anything than there may be a transmission issue. Speed sensor or shift solenoid is most common items to fail on the transmission, but it may be more severe than that. Best bet would be having diagnostic ran on the transmission.
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Tuesday, August 24th, 2010 AT 3:02 PM

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