When you try to give it more gas at 50 mph, it starts to hesitate

Check for vacuum leaks.
Do It Yourself Diagnosis and Repair

have you checked plugs, maybe you need new one's or reset spark plug gap.

Sounds like a bad spark plug, spark plug wire. Probably the spark plug wire. They usually act that way when load is applied. It may misfire under light load and not at idle. Try plugs and wires.

change fuel filter and clean fuel injectors.pour a can seafoam to 3/4 to full tank of gas see if it help the problem.

gummed up!!! run 108 octane booster!!!!

ENGINE SURGING COULD BE WEAK FUEL PUMP, STOPPED UP FUEL FILTER,BAD TORQUE CONVERTER SOLENOID OR TORQUE CONVERTER. OR FAULTY TPS.

there will be codes stored so the scanner in use has not got the right protocols to read the ECM
Nissan products have to be set using a screw in the ECM to get to read the codes
you have to be specific with make , model , year , type of equipment to get closer

A pop and hesitation is likely a backfire. The hesitation around 40 and 50 would be in keeping with that theory. There are several reasons you might be getting backfires and hesitation. If your ECM is adjusting the engine to run too rich this could happen. Misfiring might be occuring. Timing could be out. But one of the most likely is a restricted exhaust, likely due to a plugged, damaged or worn out catalytic converter. In some cases the converter may be bad enough to be giving you some performance problems, but not yet quite bad enough to signal an error. A vacuum test can help confirm whether this is exhaust related.

Sounds like A MAP sensor or a bad fuel Pump. Good Luck

gas pressure problem very dirty filter or gas pump when you have good idle and as soon you give gas the car dies no power that a low gas pressure hope its a fixya thanks pierre