After driving for a while on the freeway the car started to sputter or jolt when the accelerator was pushed hard. It also happened a lot when we got off the freeway and were going uphill. It feels almost like it's not getting gas. The temp guage isn't registering hot, but the car seems much hotter than normal (water boiling/bubbling in the reservoir). Are these two separate issues, or is there some correlation? What should we check for/do for either problem?