I reckon it is a big jump from governor to President, even from governor of a big state like Texas. I've always heard that folks in Texas were pretty pleased with him as governor and that he did well at bringing the Democrats and Republicans together.
Regardless, being governor is better preparation for the Presidency than being a Senator. I heard someone on TV say that being a Senator is being only 1/100th of half a decision. Being governor forces the candidate to make tough, visible decisions.