real funky issue when driving at highway speed for 15 miles or more

What is your question?

1995 ram 1500, 5.2. got 134k miles on it. this has happened 3 times now, if im driving at 65 or faster, after roughly 15 miles, i lose all power. the entire truck shakes under attempted acceleration, it wants to just bog down, and it back fires terribly. might be unrelated, but before this happens i lose heat also. ill turn the truck off and let it sit for 15-20 minutes, turn it back on, and it drives fine again. im also using quite a bit of oil, about 1 quart every 1000 miles, so plenum may be another issue. anything i can check? i have an oxygen sensor and cat delete coming in just to see what happens. the motor and computer is not throwing any codes. only modification is a flowmaster 44 muffler. thanks in advance.