We have traveled Hwy 57 four times back and forth in the last year. It has gotten worse and for several different reasons, all of which you have mentioned.
Our biggest delay was in December on our way to Jalisco. The paisanos were heading back in droves and there was an actual back up of traffic at the Parador San Pedro for miles solely due to the sheer number of vehicles entering and exiting the rest stop to buy food and fuel.
The road work is second with the checkpoints coming in at third. The highway has improved considerably and lets hope it gets better unless our new president decides that his austerity program should also include federal highways.
The alternative would be the highway from Saltillo to Zacatecas and beyond. They say it adds an additional hour and a half but with road delays on the 57 it could a tie.