Help Diagnosing '02 Eclipse possible misfire?

My gf is having trouble with her '02 Mitsubishi Eclipse (4 cyl) that she believes to be from rust in her gas tank but she's not mechanically inclined and I'm not sure where she heard this from. The problem seems to generally happen when the gas gets to 1/4 tank, especially on the highway. She just says the car won't accelerate and even struggles to maintain speed on the highway.

I've driven the car and haven't had any problems besides a little shimmy above 65mph probably a weight fallen off a wheel but it always revved freely and accelerated fine, etc. It did have CELs we checked and she has the slip with her but it was something about EVAP emissions, 2 seperate errors/malfunctions for camshaft position sensor, and one for crankshaft position sensor. Advanced sells both sensors for $100 each, I can get them both on rockauto for $80 total.

What's the proper order of hunting down and fixing these problems?

Clean the fuel tank and pump filters. Evap may have a leaky hose at the tank, letting crap into the tank. Sensor cel's don't always mean the sensor is bad, What caused the cel; ? Both sensors are simple voltage readers. Cam timing, Belt, can cause a light. Crank walk can cause the flywheel to hit the sensor. So before throwing parts at it, find out why.

Thanks. So you think this sounds like a fuel problem?