Carefully Measure the Rt Main Bearing Clearance (with a Dial indicator)... If it has more than Specs, the oil-feed passage under the Rt Main bearing Quill may be blocked..and that also means the Rt Rod will be starving for oil too.. If the Transmission is over-full, it may be engine oil, from that Rt main/Seal, because of excessive bearing clearance..
Put a Load on the PTO and see if it engages or Slips.. Look at the oil in the PTO..it should be 10 Wt oil... If it is 90 Wt, the seal is out... Power Steering..?? Does it work easy both ways..?? Signs of Leaking..??
Intake/Exhaust manifold going bad..?? Gaskets out where it meets the Head on each side..?? (Requires pulling the Head and having it Machined)... Not uncommon for the Intake to be splitting, where the Heat-Crossover meets the intake.. Gauges work..?? Tires..?? Radiator..??
Make sure EVERY Gear is good...and the shifter feels secure and tight.. Would be best to put a Load on it in each gear, actually..
Sheet Metal decent, or beat up..?
All the usual things as well..