MPG and Increasing HP for 94' Toyota PU 4WD

Hi, I'm new to this Tacoma World!

4 Years ago, my father and I bought this truck, 1994 Toyota PickUp base with 22RE 2.4L InLine 4 with lift up about 3 ft 1/2 and we kickin 33" tires in. Last time 22RE got blown engine WITHOUT RPM but I figured out it was oil suck in from bottom tank with net was stuck. We paid 2 grands for new 22RE engine with some performance and added RPM in too on last summer. I have tested top speed my truck can go is 90-99mph (with GPS not speedometer) but it is not exactly 99.9 or 100mph with flat highway in VA. After holiday I drove back to school in Rochester, NY (RIT). One thing I can feel and decrease speed from MD, PA, and NY is hill on highway. When hit on uphill, speed started decreasing. Any Idea how it can keep stay stable with 70-80mph in 3rd, 4th or 5th gear?

Here's list we plan/add performance parts:
- PaceSetter Performance 86-2800
- planning to add K&N Air Filter 57-9008
- planning to add PaceSetter Performance 70-1184
- planning to add PaceSetter EFI????

I have a question about increase HP and more MPG fuel save,
- We added PaceSetter exhaust (PaceSetter Performance 86-2800 - PaceSetter TFX Performance Kat-Back Systems) but I need to know how much HP the Pace Setter exhaust kicking whole ass up?
- Is this normal, 35psi all tires?

And one thing about speedometer, When we added 33 inches tires,
20mph = 25mph
50mph = 56mph
60mph = 70mph
70mph = 80mph
80mph = 95mph

How can I change back to normal than +5 to +10 mph? We have computer control for vehicle.

This Attached Picture describe:
first picture is my truck and second picture is my friend's 2011 toyota tundra with modified and he from New Jersey.