Why does my Chevrolet Blazer misfire when load on engine(acceleration or uphill)

What is your question?

Car has been used heavily in last year due to job commute. Had an oil pan leak that was repaired in August 2012 as the mechanic said it was caused by a "striped" oil plug. Instead of changing the oil pan, he welded a new "nut" that fit another plug. Oil change in February 2013, Service engine light came on during commute trip home. (32 miles) Took it back for tune up (new plugs and wires) Engine is now "ticking" loudly when idle and also misfireing (jerking) when going up any small grade change in hwy and obvious when accelerating or going up hills. Had fuel pressure checked and mechanic said it was at "65". I asked that he change out the fuel filter and he said it didn't need to be done. ?