I start out with 2000 rpm and quickly drop to 1500 rpm. No matter what I do with the shift lever manual up and down, it stays right at 1500 rpm. It'll get up to highway speed, but very slowly. the engine runs fine, but the tranny won't let it get above 1500 rpm until I reach highway speed. Battery is fully charged, and I already disconnected at left neg and pos cables connected together for 30 minutes. Also, the bottom center warning light (EML?) stays on. The only code I get is P1850.

 

Moving this to the Stock Problems/Issues section, hopefully you will get some responses.

I think that code is the "Transmission Transfer Case Contact Plate B Circuit Failure."