2008 Ford F-350 6.4L Powerstroke Resuced Engine Power Problems?

So Started the other day the trucks coolant temp gauge spikes Oild temp gauge shows dead centerno check engine or wrench, message display center showed coolant gauge symbols and says reduced engine power. I pull over **** truck off, get going again does it again. No check engine no wrench no codes. I replaced thermostats Andy did not solve issue.

Any ideas

2018 Ford super duty 350 lariat or 2018 Ram 3500 Laramie?

I like both and have always been a Ram guy. The Ram is cheaper but is the out going model year. I'm a big fan of the Cummins and the new sport packages ram offers I like. I like the ford interior and space. The digital dash is cool. Price is more, powerstroke gets worse fuel economy.

Ford F-250 or Ford F-150?

2003 F-250 XLT Crew Cab, Fx4 package, 112k miles 6.8L V10 Triton.
Or a 2006 Ford F-150 Lariat, Crew cab, 4x4, 120k miles 5.4L V8 Triton.
Which one would you think is a better option?
I'm not towing very often and when I'm my dad lets me use his truck.
I'm talking more about reliability, safety, and best truck for a 18 year old male, (myself)