Need A Little help Please

I would not mess with the gears until you find out why you are down on power (because you are down on power). Once you find the power you probably won't want to change the gears.

For what its worth (kinda like what justinp61 said), my 408 (ported eddy heads, 264/268 solid cam) runs 6.5's @ 104 mph at 3250# through the mufflers, also with 4.10 gears and 28" tires. I believe you should be faster than that once you find the culprit that is holding back the power, considering your cars weight....no gear change necessary.

My guess is you don't have enough compression for that big cam (or the cam is installed way off). Good luck.