F350 tranny problems, Please Help

I have a 91 f350 automatic 7.3 diesel non turbo. The transmission is not factory and at one time has been replaced with a jasper transmission. My problem is it is slowing shifting from 1st to 2nd gear. Then after it goes through drive and o/d, without warning the engine tachs up real high and seems to have dropped back to 2nd and i have to slow down, pull over, shut it off and then start all over and head back to the house to avoid a tow bill. Is this the torque converter, I keep hearing that's my problem. Thanks for any info or help. I've already changed the filter and fluids and if I have to pull the trans, I only want to pull it out one time if possible.

The torque converter's job is to provide a fluid couple from the engine to the internals of the transmission. If something is wrong with the converter it will make noise/vibrate, the torque converter clutch will not lock in or pop in and out (500rpm difference max if it has one), have lack of power/no power, or leak. I'm not sure about your trans as far as how/what operates it as far as the electronics or lack thereof but it sounds like it is defaulting to 2nd/3rd due to heat or slippage.