I have a 91 Mazda B3000, identical to Ford ranger. My transmission lost drive and reverse. I can only drive in 2nd or 1st. Is there any kind of fluid like slick 50 or something to fix it or possibly anything without having to either rebuild or replace the transmission??

 

You likely have a A4LD transmission. Do not put slick 50 in it! If the problem started all of the sudden, an additive likely will not help. The only products as a last resort would be sea foam to clean up a sticky valve body. Did you check fluid level and condition?
Easiest thing to check is the vacuum modulator. Make sure you have a drain pan under it. Pull off the vacuum line attached to it. If fluid comes out it is bad. With a bad modulator, fluid will get sucked up and burned in the engine, gradually draining the transmission. If you drop the pan, a lot of debris in the pan is will likely indicate a need for an overhaul.