I just rebuilt my 904 trans in my 69 dart. I filled it up to the proper level of trans fluid. I took it for a ride but the darn thing wont shift out of first gear. The main pressure readings seem to be in spec but the govenor pressure readings are real low. could i have put the govenor in backwards?

Sounds like you have done the pressure checks.
The low govenor presure could be from a mis-asembled govenor assembly or the sealing rings on the output shaft.
You may want to pull the tail housing off to see if the problem is in the govenor assembly, if it's sealing rings, the whole trans needs to come apart.
DD

I pulled the tailshaft off and the govenor seemed to be ok but the inside felt granual. I dropped the pan to find what looks like a pile of dirt in the bottom of the pan. the filter is filled too. I forgot to flush the cooler I am pulling the trans back out. Thanks for the info.