Chevrolet Repair: Sticking speedometer, lane blacktop, autohelp

Question
I have a 97 Tahoe 4wd 5.7L automatic. Recently I have noticed the speedometer sticking at 50 or 55 when passing on two separate occasions. Last week it stuck at 50,the third time,and the transmission wouldn't shift out of passing gear. I'm not normally a parts changer and prefer to test and trouble shoot but I didn't feel safe with the testing method so I replaced the speed sensor in the transfer case. I should also mention that when I pulled over the engine RPM's stayed about 2500 until I shifted to neutral and the speedometer dropped to 0. The same problem happened again with the new sensor only this time the speedometer dropped before coming to a complete stop. There is no engine braking when I lift, the tranny seems to go in neutral and if I hit the gas again it's like dumping a clutch as the RPM's zoom til the tranny starts pulling again. The problem seems to occur only in passing gear as I have passed without it kicking down. This is on two lane blacktop with long and short passing zones.
Can you help?
Thanks,
Mark

Answer
This is going to take some hands on technical diagnostics with special diagnostic meters in order to determine if your problem is internal transmission related and or a problem with the vehicles computer system as most of today's vehicles transmissions are controlled via electronic solenoids turned on and off by the vehicles computer. the speedometer is also computer controlled.


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