This started about a month ago, and I cant find a short or a bad bulb. The fuse does not blow right when I put it in, I can drive for about 5 min or so going about 20 mph, than if I go any faster The fuse blows. Can this be caused by a short, I cant find one. Could this be a bad/loose ground. It only blows when I speed up past about 20mph.

 

defiantly sounds like an intermittent short somewhere.
it could be a wire rubbed thru or a bad light bulb.
look under the back and see if it has had a trailer connector put on it.
the bulbs can look ok, but still have a problem.

on the wiring, you'll need to pick a place and start going over it looking for a bad spot. you may be looking for a very small nick where the wiring goes around a piece of metal or near a screw.
it could be anywhere, where the harness runs under the carpet/rocker cover, in the back, under the hood, around the front bumper, side lights, license plate and so on.
on the harness, i would check the easily accessible places first.
because with a wiring problem you may end up having to inspect the entire parking light harness which would be very time consuming, once you have checked the easy places, you may want to replace all the park light bulbs next.
that includes the front, side markers, and license plate lights.
good luck