Re: f 250 7.3L help please
If the wastegate isn't letting out the additional boost, the engine will carry the burden and overheat.
If the coolant has been in the truck for 6 years or longer, regardless of miles, flush it and replace with fresh coolant mix. Diesels are iron blocks in almost all cases (some newer ones use thick aluminum pistons), and iron rusts; even more so if you only use the truck for short trips. Remove the coolant/rad cap when the engine is cold. If you see any white goop, or small chunky crap around the edge, you need a coolant flush. A flush can also dislodge built up particles stuck in passageways that help cool the engine. To elaborate more on Logan's post, the water pump impeller (fins) can rust and deteriorate lowering proper coolant flow throughout the block.
I'd advise this as a last resort, but if winter weather isn't an issue you can change from a 195F thermostat to a 185F that should keep temperatures in check.
If you have yet to get the transmission serviced, do it once you manage the engine temperature problem. I mention it only because heat is the ultimate enemy to a transmission. An engine that is consistently close to running in the red also warms up the transmission, even more so if you tow/haul/off road the machine.
'11 Ram Quad Cab 4x4 SXT 5.7L HEMI (stock); 48,500m
'06 Pontiac G6 GT 3.5L 220hp; 64,000m
'12 Chrysler 200 Limited 3.6L 283hp; 28,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!