This gasoline K25 engine will not accelerate when put into forward or reverse (no visible codes). The truck revs in neutral, or using hydraulic functions in neutral. The oil light is on and sometimes goes out, but oil level is good, but dirty. Truck temp. is mid-range. The operator said, the truck needs to idle for about an hour, then it will accelerate in gear; if shut down, only for a minute, it will not rev in gear again.

Perhaps a bad oil sender is throwing the truck into a "slow mode?" Maybe old oil has thined out, not allowing the sender to read pressure well enough? Perhaps the oil pump is faulty? Could be everything, or has nothing to do w/oil.

Any suggestions?