Jcb 532-120 1998 will only drive forward in 1st and 3rd gear but will drive in reverse gear in all speeds

Here is a forum from Chevrolet talking about the trany problem.

https://chevroletforum.com/forum/silverado-fullsize-pick-ups-21/700r4-lost-forward-gear-but-has-reverse-31282

Greetings, I read your question and I think Reliable-Store can help you in this. Here's the site link.
Jcb Service Manuals

From what you are describing, it is possible either the 3-4 actuator is no longer playing with the 3rd & 4th clutch packs, only way to know for certain is to hook up the good ol' pressure gauge to trans. system, yeah, you think the Chevrolet dealer should know this right?

Sell it now if you can!
Smiles

Check the fluid, with the motor in park.

I have a 92 Crown Vic first and second works fine reverse works fine when it shifts in the third gear it goes to slipping and overdraft can you help me fix this problem thank you

Are you sure you have all 4 forward gears? Most of the time a no reverse condition also means 1st and 3rd only.No 2nd or 4th.If you dont have all the forward gears as i suspect , the reaction shell is stripped or broken.If you do have all the forward gears then these are the two most common reasons you do not have reverse.1 reverse input clutches are damaged or burnt 2 forward cltches have slipped to the point they are welded together causing a mechanical bind in reverse and also causing the transmission to pull forward in neutral.Let me know if i can help.Good Luck.

if any where on the veicle it says AWD it is supposed to always be in 4 wheele drive if it says 4x4 than try driving in reverse and then going through the 1st 2nd and 3rd gears forwards and see if it works.

Sounds like a linkage adjustment problem

It is an internal trans problem. I build transmissions for a GM dealer. It is going to be the input carrier, forward sprag, and 3rd/4th clutches. I have seen several. Get it to your dealer. That truck has a 100,000 mile powertrain warranty. That includes the trans. Good Luck.

U are going to have to have the trans torn down and replace the reverse clutch drum.