Nope; can't be fixed!
Of course it can. That was sarcasm. Suspect a leaking vacuum modulator. It has a vacuum hose hooked to it, and the transmission fluid is getting sucked into it, then into the intake manifold. The vacuum changes according to load on the engine so it is used, along with road speed, to tell the transmission when to shift. When the unit is leaking, little vacuum can build up in that line, and low vacuum is what you get when you push hard on the accelerator to take off fast, pull a trailer, or go up a hill. Those conditions make the transmission wait longer to up-shift, and it's the vacuum modulator that is responsible for telling the transmission what the engine load is. Yours is incorrectly telling the transmission you're under hard acceleration. That's why it won't up-shift.
GM used a vacuum modulator on all of their vehicles for decades. Chrysler never used one. They used a simple mechanical linkage hooked to the throttle. Ford used half of each system, depending on year, model, and which transmission was used.
Rather than trying to describe what it looks like, buy a new one from any auto parts store, then look for that part near the rear of the transmission. A single bolt holds a forked metal bracket. Remove that, then the modulator pulls straight out.
Tuesday, June 3rd, 2014 AT 9:06 PM