I have a 1988 Chevy C1500 Silverado pickup truck with 64,700 original miles on it. I inherited the truck in 2017 and aside from some minor repairs, it has run quite well. The truck has a 350 engine and an automatic transmission. I use it mostly as a vehicle to haul relatively light loads when needed such as brush piles to the dump, lawnmower, etc. Occasionally I will take the truck out just to run it around, keep the battery up and seals lubricated. The other day, I took it out and noticed an unusual thing with the transmission. When I get the truck up to highway speed (50+mph), the transmission is acting like it is shifting from "Drive" to "Overdrive" rapidly, especially if I am pulling an uphill grade, even a very slight uphill grade. When I shift the transmission from Overdrive to Drive, the behavior stops. To my knowledge, the transmission has not be serviced (filters, fluid, etc). Since transmissions are considerably above my paygrade, I will probably take it to a shop that specializes in trannys. Any thoughts, based on symptoms what the problem might be and if so, what will be involved in repair.
it's either "hunting" between 3rd and 4th, or the torque converter lockup isn't working properly
Either way, it's an internal problem and best left to a professional.
The only thing a driver can do is maintain the fluid. There are no electronics on this transmission.
Thanks @mountainmanjoe. I plan on taking it to a repair shop locally that specializes in trannys. One thing I will insist on, they DO NOT flush the transmission. They can replace the filter(s) and replace the fluid in the pan but NO COMPLETE flush of the system.
if the fluid needed to be exchanged to correct your problem then I would do it
UPDATE- Took it to a shop that specializes in transmissions. The owner and I took the truck out to verify the problem. He immediately said it is NOT the transmission. He was sure it was a "miss" in the engine, either a spark plug wire or the rotor cap. The truck also had some brake issues in that the rear drums and front discs were warped. Also had some bearings that needed replacement. While the brakes would stop the truck, they "pulsed" when you stepped on the pedal. There is no doubt in my mind the work he did was needed and he was not simply running up the bill. This shop has been around for 30-40 years. Fairly quick turn around on repairs. Dropped it off Tuesday morning and the truck was ready on Thursday morning. After repairs, I took the truck out for a short run and it ran and shifted smooth as silk. Brakes were totally smooth as well. This shop gets an A+ grade from me.
I'm glad you found a good shop and that it was a relatively easy fix. I can see how a misfire could feel like a jerky transmission. Thanks for following up.