Using 8 3/4 with /6

Ok now we are on the same page.
So what you really need is a TC and probably gears.(as others have stated)
Or to swap out that cam.

IDK what gears are available for the 7.25, but I'll wager yours has 2.76s which are nice hi-way gears. Your slant does not need a bigger rear end like the 8.75, nor the 8.25. However if one fell into your lap with the appropriate gears and a SureGrip,for a good deal; then of course you should jump on it.But there is no other reason to ditch the 7.25.
But above all, you will probably need a higher stall TC.

I couldn't find specs on that cam in the link you sent; but it is titled as a 268. If 268 is the intake duration on that cam, then that is a pretty big cam, and unless the engine was well engineered around it, it will certainly be soggy on the take-off. So before you spend any money at all, you need to do 3 things.
1) do a compression test and print the cylinder pressures here.
2) do a stall-test
3) determine the current rear gears.
From the results of those we can see where you are at,why it is soggy, and what to do about it.