sounds to me like either a fuel system issue or a vacuum leak.
this an LPG truck? or gasoline powered?
on the LPG engines:
I'd check the pressure from the EPR, check the throttle body and intake for vac leaks, make sure the air filter is clean, check all vac hoses.
on the Gasoline powered engines
check the injectors on each cylinder and make sure they are all firing, check the throttle body and intake for vac leaks, make sure the air filter is clean, check fuel pressures.
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