I find it somewhat baffling. Maybe I should rebuild the entire engine and that will boost it up. Also modify the PCM

yea but that viper engine doesnt redline near as high as ur jap motor...its all juss a balance...plus american manufacturers dont push their motors as hard as other countries for sum reason...case in point...the new bmw m3 has a 4.0 liter that puts out over 400hp...new mustang has a 4.6 liter that only puts out 300...bmw has higher redline and the motor is maxxed out alot more then the stang...stupid american car manufacturers...

Besides forced induction, the 2 main ways to get more horsepower is more RPM or more displacement. More Dispacement is easier and comes with the added bonus of more torque.

I have noticed that GM cars have very low horsepower but also poor gas mileage, especially the Pontiacs

I can argue one particular exception.

Corvettes get pretty good gas mileage concidering their power. The C6 is rated at 16/26 mpg on the new more stringent 2008 testing method, which is pretty good for a 436 HP. The 505 HP Z06 is rated at 15/25 mpg. You'll be hard pressed to find another car made by anyone that has that kind of power and that kind of gas mileage.

but if you look at the Solstice GXP has around 220 hp and around 19 mpg, I find that negatively. I don't know the exact specs but I hear the Aveo get horrible gas mileage cosidering it's size and output.

The Aveo is rated at 26/34 mpg on the old pre 2008 mpg testing standard. Which I agree is good but not spectacular concidering.

yea, i believe it is classified a sub-compact and has less than 120 hp. Other cars in that class usually get above 30 mpg. Especially the Japanese kei cars like the Daihatsu's and Suzuki Cappachino, Honda Jazz, etc.

My 5.0 get's 24mpg

that's pretty good considereing it's size but what's the horsepower on it? what mods are on it?

3.27 gears, JBA equal length shorties, offroad h-pipe, flowmaster 2 chamber catback, ported E7 heads.

mostly exhaust mods then, that improves fuel efficiency by reducing back pressure and also frees up more horsepower. The gears, is that the a transmission gear or final gear?

umm not really. The 3.27 gears are what makes the gas mileage so good. Most of the time when people refer to 'gears', they mean rear end gears lol

3.27:1 final gear ratio isn't bad

It's a highway gear. Hence the 24mpg. I will soon get some 3.73's or 4.10's. With 3.73's I will get around 21mpg. 4.10's I'll get around 19mpg.