Dutchef

My oil pressure on my 96 gmc 454 7.4L seems a little high. Highway driving at 75mph is about 55psi. Spec says what? 15-24? Could the 5w-30 be wrong? Oil pressure relief valve stuck? If so where is it located? Also have some intake backfire pop at start up only once then it fine...Iv changed everything...plugs...distrib...fuel filter...o2 sensores...maf.etc...next step i thought to change the cat. No codes. thanks for any help.