i got on the high way last week and my truck shifted to 2nd to pass someone going about 65 mph and it was screaming at like 6000 rpms. normally it limits at like 4.5 rpms if i floor it and this time it was bouncing at 6 which is the max that the tach reads, then it slammed into 3rd and continued this for about 3 miles, the speedometer dropped to 0 when i was going about 70 and then after a couple minutes it was fine. i checked the trans fluid when i got home and it was almost dry so i filled it back up and thats when i found the leak. my bolts in the trans pan were torqued to about 1.5 ft lbs instead of 8.3. i changed the gasket and filled the fluid up and it seems like the leak stopped but my speedometer still dances around when i hit the brakes, its fine when i speed up though and i have one of those crazy shift issues like once everytime i drive it, and the overdrive light flashes and then all of a sudden its alright.....any ideas?

 

Don't know if you found an answer to your problem yet but it sounds exactly like a problem I
had recently. It turned out to be the speed sensor on the transmission that sends speed
info back to the computer. If the computer can't track accurate speed the truck will do some
crazy things. I had the speed sensor changed at a transmission shop for around $100.00.
So not too expensive to fix. I'm sure I could have done it myself for a lot less if I would
have known what the problem was.

 

i agree. i think it's your speed sencer. it should be located on the tailhousing of the trans. or on the rear axel depending on the year of truck. also check the wires that plug into it as they may be damaged and getting a bad conection.