First off, what tire pressure are you running? It depends on your comfort level, but I'm guessing 40+ psi is your starting place. I could run 40 in South Carolina, but when I came back to Michigan I had to go down to 36 to keep from getting beat up on rough roads. Stiffer springs and lower profile tires will probably keep you from cranking up the psi too high.
I wouldn't put a grill blocker of any sort on in Texas until I could watch my coolant temp accurately. I've got the lower blocked off on my Mustang, but again this is Michigan.
Are you keeping engine rpm below 2000 rpm between shifts? 1500 rpm? My Mustang will pull in 5th (top) gear from idle (700 rpm). not quickly mind you, but for most driving it's fine. On the highway I am stuck running 2200-2500 rpm, but otherwise it's below 1500rpm. Well, except when I want to remind myself it's a Mustang...
