my wifes 01 durango 5.9 surges at speeds between 45 and 55mph. if you are accelerating you don't notice it but if you are cruising at those speeds in town the rpm's jump. has 84,000 miles. just changed plugs and pcv valve. could it be throttle position sensor?

 

Yep that's your problem. It's a pretty common problem with the D's but if you have 35-40 bucks and a brain you can take care of it yourself.

 

Just FYI, these faulty TPS's usually will not throw a code either so have it changed anyways and your problem should go away.