I would think its The MLPS. Its the switch/sensor that controls when and how the gears shift. If not working....You may shift in and out of gear. I needed to have mine replaced because i would be doing 75 on the freeway, it would kick into neutral for just long enough for it cause to cause a violent Buck when it kicked back into drive.
Its worth it to know that you had the tranny rebuilt, and that the mlps switch is new and working properly.
I'll second the MLPS Sensor, although I believe on a 93' it's just a Neutral Safety Switch. The MLPS works in conjunction with the computer on 94's and later years. I just replaced the MLPS on my 94' and it's unbelievable how many problems that little part can cause. My transmission felt as if it was slipping over the course of a year and getting worse with time. It's basically a sudden neutral condition as described above. Anyhow, considering my truck has 215K on it, I thought the tranny was probably about shot. Good thing I have a reputable and honest tranny mechanic! Gee, how many people do you think have taken their truck to the dealer or Amaco and told they need a tranny rebuild when all they needed was a new sensor?!
jermil01: When I took the truck to my tranny guy he got no codes for the MLPS. So, when I got my truck back that left me scratching my head. I did some research on some other BBs and there were a lot of fingers pointing to the MLPS. It's a part that eventually wears out so I figured it would be worth the gamble. Paid off. Here's a link with some info on the MLPS you should find helpful: