The 1st gear ratio in a typical 5 speed is fairly low. The fact that you can run to 55 mph at only 4800 rpm does indicate you have a really HIGH rear gear. In my opinion WAY to high. I would think you could not even run 5th gear without lugging the engine rpm to low (unless your doing 100 mph
).
3.73 would give you a top speed of around 100 mph in 4th and overall with your 5 speed I think is a bit on the low side. Certainly would give you some tire spinning power all right! I'd go with a 3.5, which is more suited for the over drive trans (in my opinion), and still let you fry the tires.
The lower rear gear is a whole new ball game, a good ball game, but will come with problems. Like axle hop, loss of traction, much easier to "spin out" due to the tires wanting to break loose under power in a corner. After you change rear gears be careful driving until you get a feel for the new setup.
Concerning shift point. Yes the 302 with the cam you have starts to loose horse power after 4800 rpm or so. This is a great "torque" cam, not good for high rpm. I would recommend a shift point at 5000 or a little more because when you shift the rpm tends to drop to low for the next gear. My rule of thumb is: A couple of hundred rpm ABOVE max horse power rpm of your motor output. Granted MOST people tend to shift well beyond the point where their motor is still making good power.