2500 Van- No faster than 40 mph-??

I have a 1997 Chevy Van 2500- fullsize, auto. trans, 5.7liter. The problem- when driving down the road at approx. 30-35mph. the speedo displays 90-100mph shortly after my van won't go any faster almost as if thier is a speed limiter. I just had the speed control sensor replaced (last night) still did not correct the problem. Somone said it could the computer or the trans?? We did hook it up to a computer and no codes were detected also we drove with the computer hooked up and it read the same speed as the speedo dispalyed *the wrong speed* I will also add after leaving the garage last night my speedo now does not work at all- still the same problem. I need some advice!
this problem started approx. 2 months ago? Any help would be greatly appreciated!!!

Check speed sensor signal before and after speed sensor buffer.
Also check speed sensor signal into pcm/vcm.
Could be in buffer or pcm/vcm.
MT

I will have my mechanic check- Thank You!!

Good luck and let us know how it goes.
MT

My mechanic is busy is there any way I can check this myself-if so location of device(s). Also this may be a crazy question but I can purchase a reman. ecm/computer for $100.00 with a one year warranty- DO you think this would solve my problem- my mechanic said it should but he also said it could be the wiring going to the ecm.???

I just read something about a "DRAC Module" could this be my problem?

Thanks for the Help!!

Installed the new ECM- Van runs great again! Solved my problem!! Thanks for the advice!

You are welcome and.
Thanks for posting back how it went.
Glad all is well.
MT