1996 GMC S15 Transmission Problems

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The first step to do is to check your fluids. How long since last replacing the tranny fluid and filter? If it has been awhile then you should do that and see if it helps. If it doesn't help then it will have to be inspected. Could be solenoids worn out, may also be torque converter issue.

Let me know how that tranny fluid looks and if the new fluid helps, I will follow up.

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The filter itself wouldn't be the issue. Mainly the fluid would be the only reason as far as fluid and filter go. I just stated filter as well because you get filter changed with fluid. If fluid is clean then next step of diagnosis is to inspect transmission related linkages, vacuum hoses, and electrical connections that may be loose or disconnected. One of the most common problems are corroded battery terminal connections, so don't overlook that. If all looks OK here as well, you will need to have a reputable tranny shop run a diagnostic on the elec. Components. Since late model transmissions are controlled by a computer that operates shift and pressure control solenoids inside the transmission, the computer needs to be electrically scanned by a transmission professional to determine if any electronic control problems exist.

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Any other signs occuring while driving? Clunking, jerking when shifting out of Park?

Inspect the U-joints for wear. If OK here, you can check the resistance of shift solenoids. Use an ohmeter to check Ohms. Should not be higher than 4.5 Ohms. If it is, replace solenoid.

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Every 30,000 miles to change tranny fluid and filter under severe driving conditions (sandy roads, trailer hauling. Etc.) Or 70,000 miles under normal conditions.

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Some vehicles can't be towed on their wheels but your vehicle should be fine to tow? Below are the towing instructions for Chevy/GMC trucks.

2-WHEEL DRIVE

Chevrolet and GMC Pick-ups can be towed on all four wheels (flat towed) at speeds of less than 35 mph (56 kph), for distances less than 50 miles (80 kph), providing that the axle, driveline and engine/transmission are normally operable. The transmission should be in Neutral, the engine off, the steering unlocked, and the parking brake released.

The rear wheels must be raised off the ground or the driveshaft disconnected when the transmission if not operating properly, or when speeds of over 35 mph (56 kph) will be used or when towing more than 50 miles. (80 kph).

Do not attach chains to the bumpers or bracketing. All attachments must be made to the structural members. Safety chains should be used. It should also be remembered that power steering and brake assists will not be working with the engine off.

4-WHEEL DRIVE

Remember that the power steering and power brakes will not have their power assist with the engine off. The only safe way to tow is with a tow bar. The steering column must be unlocked and the parking brake released. Attachments should be made to the frame and to the bumper or its brackets. Safety chains are also required.

If your having issues again then it really sounds more like an internal problem and the new fluid/filter just delayed the issue some. I would suggest having the tranny diagnosed at a reputable repair shop to save it. There are a lot of internal components that can cause it to slip and there is no way to pinpoint the exact component without a diagnostic test run on it, sorry.

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