I have a Chevrolet Van Beauville 1993 G30 with a 454 V8 gasoline engine with a 4L80 automatic transmission. Because of the poor gas mileage, I replaced the engine with a 6.2L V8 Diesel from a Beauville 1986 Van. I left the computer in place and it is connected. The computer harnesses from the sensors and the distributer are disconnected. Now, the transmission is not working properly. Very poor torque... extremely slow uphill driving. What can I ***