Low HP & Fuel Mileage -- Any Ideas?

[Mike129]

Hi, all.

I have had my '98 for a bit over a year. I love it. Mostly. I have always thought it was down on power & MPG but could never prove it. I just did the emissions test and have the following results (numbers at the rear wheels, of course):

Speed Power Torque Opacity %
----- ----- ----- --------
60.2 ......140.....1304........15
50.4 ......149.....1658..........5
40.1.......138.....1934..........3

For fuel mileage I get <12 mpg city and usually <14 mpg hwy.

Both the HP and mpg numbers seem low to me as does the opacity at 40 & 50 mph, but I don't really have much to compare with.

I live in Colorado Springs at ~6000 ft., and I don't understand the impact that has on HP with a turbo. The vehicle is a '98 w/70K miles, 12-valve, 4x4, auto with a 3.55 axle ratio.

What I have already done:
- changed the overflow valve
- had the waste gate actuator replaced
- reset the injector pump timing
- replaced all of the filters (including fuel)
- cleaned the fuel pre-heater screen
- replaced the tranny (it was slipping a bit)

Most of the above that cost any real $$ was covered by the extended warranty I bought with the truck (which is lucky b/c I never buy those things, but I had a feeling this time). I do not want to BOMB until the warranty runs out in 2 years.

Any ideas?

Thanks!
--Mike