There seems to be alot of info on this topic but it's scattered about so I'm going to put my findings in one place.

My truck is a 1996 chevy silverado. One day, while driving home, I noticed it didn't shift into overdrive. I pulled over and checked the oil, which was fine. I then shifted it between forward and reverse several times. It was much more solid in reverse. I continued on my way home fearing I was going to have to invest in a new transmission. Then it suddenly shifted. I then stopped and started out again but the shifting was violent between 1st and 2nd and 3rd. I stopped at a place to run an errand on the way home and was there for about 15 minutes. It worked fine the rest of the way home. I took it to checker auto and scanned it. The code said it had a problem with an o2 sensor. I did some more research and discovered that sometimes a bad ignition switch will cause transmission malfunctions. I bought a new aftermarket one off of an ebay store for about 50 bucks. I put it on, and contrary to popular belief, you do not need to pull the steering wheel to change it. The fact that I had to unhook the battery to change the ignition switch reset all of my DTCs. It continued to work fine until about a third of the way through my 400 mile camping trip. Only this time, overdrive was gone for good. Not even unhooking the battery to reset the codes would fix it. I thought it might be the o2 sensor problem because in my research, I also found that the o2 sensor is also on the transmission circuit. so I decided to find a local checker and scan it again. This time the code PO 753 came up. The code for the shift solenoid A. As it stands now, I am going to get both shift solenoids A and B to change them out because if one went, the other is likely not far behind. And losing B solenoid will almost de-mobilize the truck. I will post back with my results.

 

Yeah when I read halfway through your post I was already considering the solenoids or a problem in the valve body. Whoever takes the pan down might need to look at all the valve body for other problems. Let us know what happens!

 

A&B solenoids are both accessable once the pan is removed. best to change both at the same time.

 

I have ordered some new ac delco shift solenoids off of ebay for 26 bucks for the pair. They wanted 30 bucks a piece form the dealer. So I will install them as soon as they get here.
So I was driving my truck home from work last night and the engine just killed on me mid flight. I'm assuming it tripped into a failsafe mode possibly due to the other solenoid going out? Any thoughts?

 

Its possible. Have it scanned again to make sure.

 

While I was at the auto parts store getting a transmission filter, another guy there overheard me talking about how my truck wouldn't start. He suggested that the problem was my pickup coil. The thing he was referring to is actually called the cam shaft position sensor, and is a small black box located under the distributor cap. Apparently a vent hole gets plugged up and prevents fumes from the distributor operation from venting out and burns up this device. I changed it but it was not the problem. However, it may be a useful tip to others who are experiencing problems. They say that when the sensor goes bad, you can tell because the resin on the bottom of it looks burnt and is bubbling out. My transmission shift solenoids arrived and so I changed them. I tested continuity on them and one of them was definitely burned up. After changing them it still would not start so there was no fail safe mode that it went into. I then pulled off my fuel filter and it was almost plugged solid. While I had it off, I checked to see how full of a stream my fuel pump was pumping. It was pumping a full stream. I put on a new fuel filter but it still wouldn't start. At this point, I either needed a diagnostic tool, or a fuel pressure checker to diagnose it further; both of which I did not have. Nor did I know anyone who would lend me one. So I had it towed to a shop. After a week of waiting for the mechanic to get to it, he found that although my fuel pump was pumping good, it was only putting out 13 PSI. It needs to be at least 55 PSI. I assume that the plugged fuel filter over stressed the pump and ruined it. The mechanic changed the fuel pump for me and the truck started right up. The transmission has also been working just fine. I have decided from this experience that the most likely problem is the most obvious one. (and quite frequently the most expensive one.) Anyway, I hope this helps others with issues they may be having with their vehicles.