I recently hit 50,000 miles on my '04 Ascender and have had nothing but problems since. I've already cleaned the throttle body, replaced the fan clutch, and tested the APP sensor. The SES and REP lights seem to turn on at random and the only code I'm getting is the same P2138 every time. I tried running it with the fan clutch unplugged before I replaced it and still had the same problem. The new fan clutch also seems to stay locked up after every startup until the engine goes above 4,000 RPM even when cold. I'm thinking that it could be a damaged or corroded wire somewhere but I don't know where to start beyond the harnesses for the fan and throttle body.