Hard shift, won't shift unless high rpm
 

I have a 1990 2wd Blazer, 4.3 engine, that won't shift unless I run the rpm's up between 3500-4000, then I have to let off the gas and immediately pat it to make it shift. I got to third, but didn't try for o/d... the speedometer is not working, which is likely the sensor. Could the sensor be the problem? I dropped the valve body, and nothing seemed stuck. Thanks in advance!

Also, I need to know if the speed sensor from a 1992 4.3 caprice will work with my computer and digital dash. It seems someone swapped trannies... or do I need to swap the tail housing and sensor drive back to the magnetic setup?