deserttoy

Trans shift selonoids

I drive a 1996 T100 4X4 automatic transmission with 330K miles. The motor has been rebuilt, but unknown transmission work. A few months ago, it started slipping out of gear while driving. Once I released the accelerator, it would go back in gear. It has been getting worse lately. I have had it in to a local Tranny shop, and spoke to a couple others. Of course they want to rebuild it completely. I had one of my mechanically inclined friend drive it yesterday, and he noticed that the slipping does not start until it has been driven for about 10 miles, and happens more when climbing the slightest grade. The shifting is tight in the beginning, but once the slipping starts it gets worse the longer driven. When accelerating from a stop it shifts from 1 to OD rapidly. He is not familiar with Toyota mechanics, but suspects it may just be a bad or worn Torque Converter. After test driving we checked the Fluid level, and it was just below the low mark. We added a half quart of Dextron II, bringing it to full, took another test drive, and it had improved, but still slipped a little. I have added fluid several times over the last couple months, but it does not appear to be leaking. We did a "stall test", and the rpm' went to 2000. We could not find any factory spec.s for what it should be.Turning the engine off and restarting also seems to lend a temporary fix to the slipping. My cruise control works intermittently too. I am stumped. Check engine light is on, ant throwing code P0500 Vehicle Speed Sensor.
My neighbor had a wrecked 94 4Runner with auto trans., and offered the solenoids out of it. When I went to my local NAPA store, they listed the same solenoid for for both vehicles. We pull the solenoids out of 94 4Runner, and installed in 96 T100. At first there was a little slippage when cold, but improved to no slippage on the first test drive. Two days later, the slippage is back, and almost worse than before. I did not test the 4Runner solenoids before installing, but thought I might test the ones we pulled from T100. Can you run me through how to test?
Also, when I drained the fluid from T100, I expected 2-3 quarts of fluid to come out, and placed a 1 gallon container to catch. It was soon overwhelmed, and much fluid went to the ground. I'm not sure how much came out, but when I refilled with new, I put 1 1/4 gallon back in. Does this seem correct? According to the stick, I am at the correct level. I am questioning if I have the right dip stick. I noted that the stick from the 4Runner was about 2" longer than the T100. Could the slipping be a symptom of overfill?