they do have crappy gears stock. The 5.0 is a low peak motor in stock form and doesnt make very much hp, but has a good bit of tq. You will top out earlier but your 1/4th mile time will be faster with 3.73's vs the stock grears which are probably 2.73s~ if its an automatic there is another major source of sluggishness.
You can wake up the 5.0 for very cheap with heads/cam/intakes exhaust, cai, gears, suspension upgrades to hook up (important).
If its an auto I would suggest swapping a t-5 or selling it for a car that has one
as the auto is great for consistency byt the AOD sucks in stock form.