Doing a little assuming, i.e. frontal area equal to approx 6 ft wide by 5 ft high and a CD (Coefficient of Drag) of 1.0 (which is probably very optimistic for your truck) to go 200 you will need somewhere in the neighborhood of 1650 HPS! with 800 you would go approx 155- 160 mph. The formula is:
HP=CD X Frontal Area X mph(raised to the power of 3) /146600
So do what ever you can to lower the frontal area, i.e. lower the truck to a 2 inch ride height, chop the top, narrow etc. and do what ever you can to lower the CD, close of the radiator, cover over bed, remove anything that sticks out into the airstream etc. will help also you may want to go for some propane and a compound turbo system for some more HPs.
Looking at the gear ratio thing you would need a 1.57: 1 ratio, using 33 inch tires. (MPH=RPM x tire dia in inches/gear ration x 336)
Since you sound ready to spend some real money, contact Dick Holt at Holt Machine, Santa Ana CA. He makes big power quick changes with ratios in the 1.5 area. Theses are good for 1500 hp+. I don't have his telepohone number but I am sure that someone will provide it.
It is only money!!!
Rex