Is there a programmer that would lock up converter in 2nd gear under full throttle? Trans shop owner is saying part of a problem after rebuild, is he full of it?

 

I don't know the answer to your question, they do adjust line pressure, but i'm not into it enough to know if that's the same thing. I do know that my truck shifts really weird under full throttle until it reaches 3rd. It shifts into OD fine under throttle. I wish I knew how to get it to shift firmer. My predator has hard shifts, but its not enough on the higher settings, or propane.

 

My Bully Dog 4 bank sure has some firm shifts in Tow mode but in the higher settings it seems to be less but better than stock.

 

Many/most of the shift characteristics you guys are talking about are often part of the original pcm programming, which is changed when you install a chip. (I admit that I don't know enough about tuners to know whether or not they change the actual box code, or merely add fuel, alter fuel timing, and increase line pressure.)
On my truck, with the chip turned off, I have the same wierd shift characteristics that I had from the factory: delayed shift into 3rd, torque convertor lockup occurring immediately after the 2-3 shift, torque convertor unlocking as soon as you took your foot off the throttle, etc. When my chip is in either of my optional programs, I get a whole new set of characteristics: the shift points are evenly spaced, torque convertor lockup happens midway between the 2-3 and 3-4 shift, the torque convertor stays locked when my foot is off the throttle, until I touch the brakes, etc.
Since I never drive my truck with the chip switched off, I'd forgotten how lame the original programming was until I drove a friend's truck that doesn't have a chip. The chip changes the entire personality of the truck, and once you've had one, you'll never go back. The secret, of course, is to know which box code to have loaded into your chip, to give you the characteristics you want. Most chip programmers know which code will work for you.