My 98 bravada is fine in the morning when I first start to drive it but after about 20 min or so it starts to sputter and also sputters while it's idling. Does this sound like it could be a plugged cat or sensor? The fuel pump and filter are about 2 years old and I hooked up my obd2 tester and there was no codes as also the check engine light has not come on. Anyone know what this could be or where I should start? Thanks in advance.