Might be the PMD
Might be the pump mounted driver (PMD), that is, the black box mounted on side of the fuel injection pump. It gets hot and then won't do its job. Do a search through the 6.5L td forum on the term PMD. It should bring up lots of info on symtoms of this little black box failing.
Black 95 6.5TD, 929 block, 173k miles, 65k on IP, 48k miles on self-rebuilt engine done in '09, 6 L&S Full-torque inserts in outer main crank holes, Clearwater heads, Fluidamper, rebuilt NV4500, 3" downpipe, 4" exhaust, no cat, dual T-stats, 9 blade fan, spin-on 180 degree clutch, Heath hi-flow water pump and turbomaster, PMD relocated, OPS relay mod, Heath PROM upgrade, and Kennedy headlight harness upgrade soon. Now use semi-syn Lucas 2-cycle oil every fill-up which greatly reduces the frequency of DTC 35-36 codes the PCM/ECM throws.