I have a 1993 Chevy 2500 6.5 turbo diesel. My problem is after driving in the city for approximately 5 miles, the transmission begins to have trouble shifting out of 1st gear. It will knock hard into 2nd then immediately shift back down to 1st. This occurs somewhat violently. Then the brake light will illuminate and the speedometer will fluctuate about 20miles above & below actual mph. Increasing engine speed or manually shifting into 2nd does not help. Finally, the shifting just remains on 1st gear along with brake & speedometer issue. Disconnecting the battery and reconnecting clears up the problem but it will soon recur at or about the same distant or time as before. Once I park at work, 8 hours later, the cycle is reset. This problem occurs in a variety of temperatures. Some history, this problem originally started years ago and the only symptom would be a hard somewhat violent shift into 2nd gear. Turning the key off and then back on would clear this up. Months later, it would not shift out of 1st gear after about 45mins to an hour of city driving, no other symptoms. Truck has had motor & transmission slow oil leaks for years and worked fine. Since disconnecting the battery seems to help, my first thought is that I am resetting the ECM or similar device and this may be the culprit but have read that some of these early vehicles may not have such a device or that if it is present, its function is relatively small. Please advise where I could possible start to troubleshoot this problem. Thanks.