OK Maxx, first thing. You ran your tires way too long. Once they reach around 80 - 85% wear you start to lose around a second per lap. Check your analysis figures and see.
Also, how many practice sessions do you run? If you check in the Misc tools section you will find a lot of useful info there.
Also post your driver stats in the driver section under question center.
All in all you did pretty good to get from 12th to 4th. If I see anything else I'll let you know.
Get the driver info up ASAP and we can take a look at him.