There are some dirt roads in the area, but your speed will be much lower, so a longer drive. Also, they tend to be less direct than just taking the highways.
Before you reach Carlos, head South on CR 190. It passes through the old coal mines that used to power the Gibbens Reservoir Power station in Carlos. It drops you out on FM 3090. Turn right on 3090 and go a very short distance to the beginning of CR 185. Run this almost all the way to Anderson and it drops out on FM 149 just outside of town. At Anderson, head South on CR 405 (just West of town off HWY 90). Turn left on CR 406, right on CR 446, left on CR 215, and then run 215 across FM 1774 to CR 212. Turn left on 212 and run that over to FM 1486. Then run FM 1486 South to Dacus and cross the rail road tracks on to Johnson Rd., which drops you out onto FM 1097 NW of Montgomery. You can either run that on into Montgomery or I like to run Bailey Grove Rd., over to FM 149, then head down into Montgomery. If you go left on 1097 just a hundred feet or so, Bailey Grove Rd., will be on your right. It is paved, as is all of Johnson Rd.