Trans shot, I think? Opinions please

It started a couple weeks ago, I put truck in gear and when I gave it gas it was barely moving, but after I restarted it it was fine, did that a couple times over the next few days then it got worse to the point I could not drive it, I had already got the stuff to do a tranny service but at this point I think it's just completely shot. It drives in reverse fine, in drive it won't go at all, and gear 1+2 it'll drive to a point but it slips really bad. It's been parked a week and I don't know if it's trashed or (a friend thinks) a new fuel filter and a tranny service will fix it, it's a 96 v6, 2wd with around 300k miles.
Any advice, input or experience with this?

O.D. light on ? Check engine light on ? Did you scan for trouble codes ? How does the transmission fluid smell ? Any leaks ? You do know that the transmission has solenoids and they are computer controlled... Have you checked the wiring harness ? Check these things first because it might not be the transmission....

No od light, just had the trans fluid changed two months ago because it would not reverse until it has been running for ten+ minutes (a friend did it and put synthetic in it which i heard was not good so they changed it again after that and the reverse problem stopped)
I topped off fluid it was about a half quart low still won't drive. And to be honest I don't know much about solenoids or any of that

I don't think a fuel filter or a trans service will correct the transmission issue, if reverse is good and forward is slipping badly the problem is going to be a problem with the forward drum inside the trans.

I agree changing the fuel filter and doing a trans service won't help I've told him that, I honestly think it's shot out. I'm scared to drop a few more hundred in it when it's already got over 300,000 miles I'm scared that the transmission shot out and it's going to waste money trying to fix it and even if I do fix it or replace it that I'm going to have a rod go through the block and over 300k is a lot FN miles especially for an exploder in my opinion then again I hate exploders so yeah, but I do have to say this truck has gone through so much lol I drove it with a vengeance and she's stuck with me, I don't wanna junk her

Have the truck codes scanned this will give you a starting point. OBDII code scanners are cheap...300K miles is not a lot, hell if that's a problem go to a pick n pull and remove a short block and transmission from a wrecked truck.....

Scan Ebay for a trans. I had my trans rebuilt about 4 months ago. If you got 300K it time if the truck is in good shape fix it. I also have a 96 with 260K and I love it.