I-10 thru Texas: as I remember, the milmarker on the East side of the state said "mile 864". THAT by it self should give you a clue.
During the winter months, it is the best...as far as RV parks and CG's being open.
Done that East to West and back again....takes 3 days. Stopping at Van Horn for the nite, then Junction for a nite, then Beaumont. It is, in parts, kinda lonely, but so....I agree, that driving I-10, Texas never seems to end.
I-20 thru Ft.Worth Dallas during the winter can be bad. (Check out the weather the past few weeks). I-20 surely is do-able during the warmer months...but strangely enough, there were NO easy-on-easy-off campground on I-20 between Meridian (Toomsuba) Mississippi and almost to I-95 (Florence, SC). Just one. Maybe one hour from I-95.
I-10 thru parts of Texas is a perfect place to use your cruise control. Just don't fall asleep.