I purchased a 2002 Ranger with 170,000 miles in 2024 from a friend and it had sat since 2019'ish. At least, that is the last time the registration was completed. After getting it home, the first couple things I did was change the battery (bad), fuel pump (bad), and spark plugs. The truck started and the engine would rev with no problems.

I knew the transmission was bad and the only gear that worked was reverse. After healing from a broken neck, I was finally able to start working on it again in the fall of 2025. Used transmission (no metal in the transmission pan) with ~75,000 miles was put in, I added the transmission fluid and changed the oil at the same time. Due to damage, I also replaced the exhaust from the muffler back. The truck is finally 'road ready' and I was trying to take it for its emissions test and safety inspection, but after the engine warmed up I couldn't get the truck to go over 10 MPH. When the truck is in park or neutral the engine will rev to the rev limiter, but in drive, it bogs down.

Plugs have been changed, so that's not it, Had that issue with an old car once (87 Celebrity).

I've seen comments online about the MAF, dirty air filter, or a possible blockage in the air intake hose, but I checked those and they were clean or I cleaned them. There was plenty of exhaust coming out of the tail pipe this morning so I'm not sure if the catalytic converter or muffler are clogged and at all possible, I'd rather not have to take the exhaust system apart again, like I did when I swapped the transmission. There's plenty of transmission fluid, and oil, and the oil pump registers with pressure on the dashboard.
At this point I am truly at a loss, does anyone have any ideas that may help me?