ya it kind of has a step down
Here is how i mounted my radio and antenna
I bolted the bracket for the radio on, the bolt and nut catches a peice of plastic under the radio area so it is really sturdy... kind of hard to explain, drop your glove box down and look in that are and you can see it.
Here is a pm i sent to a member on here, he said it helped him so i might as well post it for others too
The antenna i have is a 4' fiberglass whip from the source and i mounted it to the bed rail with the mirror mount, but i just used one had of the mount.... on the bed rail there are 2 holes already and the mount bolted up perfectly to the 2 holes
As for the coax i ran it under the truck and through a plug in the floor by the back of the cab, that got the wire between the carpet and the body of the truck, then behind the drivers side seat there is another plug on the carpet that i ran the wire out of, now i ran the wire underneath my console and out to under my radio bezel where the radio is mounted... out of the whole install i only see about 3" of wire
apparently if your coax is running through the engine bay or outside the truck you may get a static, also the power cable going to the radio is best connected directly to the battery opposed to the fuse panel or 12v outlet
I used 9' of coax for an ext cab and i had just enough wire
My reception is very good, many times when i am out on the highway i will have my squelch almost all the way to the left with no static or anything... not to sure how far out i get but i think it is pretty good.
Here is where i ran the power wires out of the truck, just cut a slit half way up the rubber gromit and put the wire in the middle of the gromit to prevent it from getting cut on the sharp metal