Transmission woes....

I have a 1989 Chevrolet Blazer 700R4 automatic overdrive transmission. I had the transmission rebuilt at 130,000 mi. About 9 months after the "rebuild", the blazer would not automatically shift when I started out in "Drive".... meaning I had to shift from 1st to 2nd....etc... manually. The warranty had expired ( of course ! ). He said he'd go back in for $5-600 more.... ? I chose not to go this route, as I did not trust that he actually did the complete rebuild the first time. Since then, I have changed filter/fluids and it shifted fine for about 150 miles. Now, it will not shift out of first gear at all. Where should I start ? What are the shifting mechanisms ? Should I change the solenoid? Is there a modulator? Any advice would be greatly appreciated as this is my family vehicle and we are stuck until I fix this problem.

hook up a pressure gauge and do a press test and post the result.
when you change the fluid did you find anny debrie in the pan?

hook up a pressure gauge and do a press test and post the result.
when you change the fluid did you find anny debrie in the pan?
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There was a minimal amount of fine metalic dust on the magnet in the bottom of the pan. ( Also, no sevice engine lights has ever come on.) Will try the pressure guage and get back. Thanx !

the warranty was less than 9 months?

WTF.....