My 1993 Chevy van won't shift pass 2nd gear - 1993 Chevrolet G20

700R4 or 4L60 trans. Both the same. Time for a rebuild. The longer you drive it the more it will cost.

Change Fluid and Filter
Add 1 Pint Of Transmission Sea Foam , Get it At Your Local Parts Store , You Should See Difference With in 200-400 miles

Need more info is the truck stock or purchased used? sounds like someone put a shift kit into the truck at some point. Has it always done this? Is this something recent out of the blue?

po785 is a shift/timing solenoid malfunction. po340 is a camshift position sensor A-Bank 1 circuit malfunction.

Remove the fluid - get a good flash light - get a very long screw driver - put the screw driver into the drain hole and force the transmission out of gear. Then remove the Transmission and replace or repair. Cheaper to replace. You bent the forks on the shift mechanism.

Sounds like you have a bad shift solenoid. Not sure if the Chevys are a solenoid pack, or seperate, but it will need to be replaced.

Have the transmission governor checked

is it parked in a steep hill, if so,try to releave some pressure off it,and try to shift it,if not,block wheels so van wont move,inspect shift linkage,if ok,undo linkage from tranny,try shifter invan if it moves ok,if not,inspectshifter and linkange,if its ok,try moving shifter arm at tranny,be careful!if it doesnt move, youll have to take oil pan off tranny and inspect park gear lock.

Happened to mine ,, Simple solution : Take it to transmission maintenance,, they clean up the mesh and fresh fluid,, will shift properly, will run like new.