The engine with water seepage, 1, is not easy to run. 2. The water tank consumes water quickly and is often short of water. The steam in the exhaust pipe is bigger than other cars.
If you don't have the above three points, you won't be able to pull up.
Maybe, 1, the air filter is too dirty and blocked. 2, the exhaust pipe is not smooth, (motorcycle speed can not be pulled up, these two points are the most common) 3, by the way, dredge the carburetor (non-main).
In addition, you can also consider whether the transmission system is lost.
It's almost 70 miles now, so it may not be a big problem.
Let's brainstorm and hope it will help.