Nissan - Altima :: Engine Refused To Turn Over And Catch When Turned The Ignition

My 2005 Nissan Altima has been fairly reliable up until the past two years, as it seems several aspects of the cars performance are starting to decline rapidly. I recently changed a headlight bulb, and upon reconnecting the battery, the engine refused to turn over and catch when I turned the ignition. After several tries, the car started and I noticed the check engine light has come on. I took it to AutoZone to get a read out, and the told me that I got two error codes: one for crankshaft position sensor and one for engine speed sensor. It's been a while since I got the readout, and I lost the paper with that I wrote the codes on, but I think the codes may have been P0335 for the crankshaft position sensor and P0725 for the engine speed sensor.

I changed the crankshaft position sensor and camshaft position sensors on my car, and the problem changed from a major problem to a moderate problem. The car performance now:

1) The check engine light is still on
2) When starting my car, I turn the ignition to connect the battery, wait a few seconds, turn to start the engine, and it takes about 3 turnover attempts before the engine catches and the car starts (inserting the key and turning it straight over to try and turn on the car often results in turnover attempts with no start).
3) When driving, the car now shifts hard at times and seems to be changing gears at higher RPMs than expected.
4) When going up a steep incline, as I press on the gas, the car RPMs go up but the car does not accelerate like it used to. It eventually shifts very hard into the lower gear and then I can accelerate up the incline at a much higher RPM rate than expected

I was reading wear these issues may be caused by a clogged fuel system, but I wanted to check with some of you guys to see what you think it may be before I go trying a fix on anything.

In terms of car care, I would say I'm fairly responsible. I get the oil changed regularly, and have always gotten scheduled maintenance taken care of as well as any maintenance at the recommendations of the mechanics I trust.