Hey zipmac22,
It could be the holster you're using. I'm in Texas as well (large city in the southeast

), and know all too much about the heat and humidity. One thing I do for comfort is wear a T-shirt when I'm carrying IWB...that keeps the holster leather directly off my skin (fat gut is more like it

). With a polo or button-down shirt untucked, conceal is just fine.
At any rate, I've tried several holsters with ALL my conceal weapons and have found I like the Milt Sparks Versa Max 2 the best; I carry an H&K P2000 SK in that one. Good luck getting one soon, though...takes a while to get one made but it's worth the wait once you have it.
I tried a Crossbreed, and while it's a GREAT company and holster, I just didn't care for the fact that the kydex rubbed off the bluing on the barrel of my H&K USP Compact 40 (just a little spot). And I've carried my M&P 40c Compact in a High Noon holster my brother gave me...I think it was one of the "Light Duty" models. It's not bad, but the Milt Sparks is just more comfortable.
So...while it doesn't solve your issue immediately, I'd consider looking at the Milt Sparks holster to see if it's more comfortable for you in this Texas heat. I plan on getting a Versa Max 2 for my M&P 40c and yes...I'm considering buying a Bodyguard 380 (my mom was right all these years...must have a hole in my head). If I do, it'll be housed in a Versa-Max 2 as well.
Just my $0.02...hope it helps.