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I have a 91 GMC 3500 dually 7.4. I recently had my transmission rebuilt and it ran fine for 6 to 7 months. I give it gas and it will go up to 40-45 mph and will stop accelerating like it goes in neutral. The rpms go up but the truck will not speed up and wont accelerate again until it drops down to 30 mph. Sometimes it will accelerate after 30 mph if I keep trying to accelerate. I notice if I floor it it will go up to 80 mph most of the time. Other times it will do it again around 60 mph. I took it back to transmission shop and they said they believe it's an electrical problem. I then had them put in new solenoids but no change. I've had a few mechanics look at it and no one seems to know what to do. What is wrong with my truck?

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  • Is it a TH-400 or a 700r4? Sounds like the pump may be not pumping enough fluid when you get to a certain speed, like either the filter is clogged or there isn't enough fluid. I really don't know, though. Does the fluid smell burnt if you pull the dipstick?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Sep 17, 2014 at 20:44
  • @Paulster2 I added the 4L80e (Electronic version of TH-400 +overdrive) tag, based on the OP stating that the transmission shop replaced solinoids and GM didn't (to my knowledge) put a 4L60e (electronic version of 700R4) in 3500 with dual rear wheels
    – Move More Comments Link To Top
    Sep 18, 2014 at 1:36
  • Can you feel it change gears? If so what gear fails? Using moderate throttle from a stop feel for the transmission shift. You should feel it shift and the RPM drop with each shift. Do that and tell me which gear it stops pulling in.
    – Move More Comments Link To Top
    Sep 18, 2014 at 15:16

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It's pretty obvious to me, based on your description that it's a transmission issue. Not sure why a transmission shop wouldn't be able to diagnosis it. Based on the information it sounds like it's not going into third gear, which could be an electrical issue, and if it is the transmission shop should still be able to fix it. There are a few specific things that can cause loss of third gear

  • Solenoid B malfunctioning
  • Quad driver module failure (replace Transmission Control Module)
  • Intermediate Clutch components (Mechanical problem inside the transmission)

After rereading your question again it might be fourth gear instead of third that's the problem. Here are the things that can cause that.

  • Solenoid B malfunctioning
  • Quad driver module failure (replace Transmission Control Module)
  • Overrun clutch reaction plates splines. (Mechanical problem inside the transmission)
  • Fourth Clutch components (Mechanical problem inside the transmission)

Again a competent transmission shop should be able to diagnosis this problem.

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