8.25 rear question

From 2.71s to 3.55s is a heckuvan increase ~31%. . This 31% is about the same per cent as downshifting from second gear in an A833 to first gear. The torque increase is throughout the operating range, making the engine feel that much more powerful at all rpms.
The downside , as mentioned, is that the hiway cruise rpm will be similarly increased, as will the fuel-consumption.
If you need more power, and need to keep the cruise rpm, or fuel economy;
then you only have about three/four choices, in order of cost;
1) a bigger engine,
2) hot-rodding your engine,
3) supercharging,
4) an overdrive trans in conjunction with a rear gear-swap, or an overdrive with a deep low.

Swapping in a bigger already good-running used engine is usually the cheapest option. And starting with a high-compression one is by far the smarter choice.
Supercharging is guaranteed to make you smile, and the belt-driven ones are quick and easy
HotRodding is the usual go-to; but sometimes takes a lotta time and the results are somewhat unpredictable when parts are just thrown together, or the bottom falls out of the budget.
The overdrive plus gears, is probably gonna be the most expensive, but can have the added benefit of decreasing your hiway fuel consumption. But don't do it for gas savings it will take many years and many miles to break even.

Gears are quick and relatively easy, and you'll never be sorry from a performance viewpoint.