I have a 1990 f150 xlt lariat 4.9 liter 4x4. One issue is that when at a crusing speed or just in park with a high idle speed or low rpm I'm guessing 1500 (dont know for sure becuase there is no Tach) the engine sputters a little bit. If the rpms are increased this goes away or if it goes to a normal idle speed. Is this a fuel injector problem or what could it be, any suggestions. next small issue is with the new tires, I upgraded to 31 in tires and when you turn extreme right or left, you guessed it, they rub a bit, is there anything I can do to fix this, or do I just have to be carefull about the way I turn as to prevent or limit that. Thanks