Does anyone have any experience with an OBD2 to OBD1 conversion?

Recently, I had my engine stroked and bored to a 396cu.in..
I switched the ECM/PCM to an OBD1 for programming purposes only.

Now I have developed some problems.
1. The speedometer & odometer are running slow. The guy that programmed it did change some gearing values but that didn't help.
2. The stick shift now has a hard time going into reverse at the stand-still,
and easily goes into reverse when shifting into 5th (not nice).
3. There is a surging (also feels like a misfire) going on when driving below 2000 rpm. (Could be just a fuel mapping problem.)

 

Make sure its set up for a 6spd not an Auto. There shouldn't be any problems going to OBDI provided the program is correct.

 

It is set up for a 6 speed.

 

When I picked up the ECM from the GM dealership, he told me it had to be programmed, but not to what extent.