4l80e transmission problem

I have a 1994 chevy 3500 with a 4l80e transmission. I run the 5.7 litre on a 300a propane system. My problem is that I have to let the rpms run high in first gear and let off to shift into second. That is if there is a second gear. I had Mr. Transmission plug in a computer and take the truck for a ride. He didn't get any codes but he said I lost second gear. I think he's wrong because I'm sure I still hear four changes. Also if I start out with the shifter in second gear it revs high in first (just like if I was starting in drive, or overdrive) exept when I let off to get into second, second comes but seems to slip badly. Any ideas?

Yea you need your tranny rebuilt They hada aproblem with them I have the same problem your tranny is shifting from 1 to 3 and the 4 shift points you are seening is 1 3 4 adn torque lock witch is 4 but your tranny is actually like a 5 speed but tq lock isnt a gear its in your converter and seems like a gear