Need Advice with MODs

I am getting ready to spend a few $$$ on improving my 2002 F-350 7.3 PSD. preformance. I have 43K miles on this truck I just install a set of gauges about 3 weeks ago. Now I want to change out the Air Intake and my exhaust. I am looking at the AFE Stage II and looking at going with MSRP 4" exhaust all the way back. I also want to put in an exhaust brake system, any recommendation. I haul a 31' 5th Wheel trailer. I will be heading to the mountains on an extended trip.
I don't want to have white knucles going down mountain side or over heat my brakes.

How much of an increase in preformance will I gain with changing out the above?

Any recommendation would be appreciated.

Sam