there is a place in vienna called slingblades, about 200 miles south of U of I. there was a place in marion but i think that it went out of business. Not sure about that far north though.
The closest that I can think of near ISU would be Anderson Ford in Clinton. It's actually a straight shot down Rt. 51 to get to Clinton, and shouldn't take longer than about 25 minutes.
I know this is an old thread but just in case anyone new is reading, I live in Bloomington/Normal and I went to Mike Post at DynotuneMP in Dekalb Illinois and got a sct4 chip and a custom tune for my 88 mustang gt convertible after i had my top end kit installed. Mike started pressing buttons and my car gained 41+ rwhp and 37 torque. It was my first time in and he charged me $350 for the tune and $200 for the chip. He said future tunes would cost less because of repeat business. I assume he might cut deals in groups. Supercharged engines cost $100 more for the tune he said. Plus he got rid of my annoying idle. I had questions. He answered every one of them and also explained why. Whats more is he informed me where i could get additional gains by changing some previous mods and then explained why. This guy is great. The car runs better than it has ever before. I couldnt be happier. Thanks Mike!