My first guess is the dual mass flywheel giving out. Pull the inspection cover and see how much you can rotate the ring gear, more than 5/8 inch means its shot. Bad things (expensive) can happen if the flywheel self-destructs and this is a known failure point.
Cure is a single flywheel with new clutch, do it yourself for less than $1000 (around $750 for a Con O, I think the Valair can be had for around $500)
'94 F250 supercab 4x4, original owner, 4.10LS, DIY elec fuel, Tymar air, Beans tunes on VA 4 position chip, Adrenaline HPOP, VDO boost/pyro/outside temp gauges, Ford digital AIC, DPPI downpipe, gutted EBPV, modded turbo ped, Con OFE, add-a-leafs front/rear, Monroe Reflex shocks, Milemarker 449SS hubs...coming soon: 6.0 IC...wish list: Stage 2's