2000 Honda Odessey in sand rail rpm won’t go past 2500

So this will be an interesting one. I have a 2000 Honda Odessey engine in a sand rail. After having my 091 transmission rebuilt, engine was put back in, and now I’m struggling with this 2500rpm issue. When I add throttle it hits around 2500 and falls off without a change in throttle position. Drops to 1200 then runs back up. I’ve replaced the TPS. Checked the voltage, cleaned the throttle body. I had a P0122 code, that’s it. I’m at a loss on what to check next. I looked at fuel trims but that’s not helpful as for some reason in sand rails they only have an O2 sensor on one bank. Not sure why but it’s common.
Any ideas on direction to go. I’m fairly mechanical but this is my first time with car engine. Sure makes it easier to work when it’s not packed into a small bay and I can access the entire thing without any trouble.