Have you had the code/s scanned to see what they are? Most auto parts stores these days like Autozone will scan the codes for you.

Without the cats you will get a CEL from the rear O2s freaking out without the cats being there but other than that shouldn't have any other ill effects, truck should run just fine.

You could get O2 simulators...

Sounds like you didn't plug in your front O2 sensors or one of them came unscrewed.

Or you put rear sensors in the front holes.

I thought front and rear 02s were same part #?

Forgot to add Klug's to that list of good tuners, sorry buddy :emb:

Sounds like you're in limp mode, which shouldn't happen with just gutted cats, something else might be going on...as mentioned above, maybe one of the front O2 sensors is unplugged?

Yes, that's another option, but they're pretty hard to find as they passed legislation that made O2 sims illegal a few years ago. Some guys also use spark plug defoulers, which moves the rear O2 out of the exhaust stream, and it seems to have worked for at least a few guys here. There once was some a thread with some pics of them, but I can't seem to find it now.

IMO, getting a custom tune is the best, and easiest way to go. You get the benefits of the custom tuning, get the rear O2's tuned out, and don't have any physical or visual evidence that anything's going on ;) :secret2:

If something is unplugged shouldn't it be like that from start up though? Sorry for all the questions

Not necessarily, some faults aren't picked up until their monitors run, and once the monitors do run, the PCM picks up the fault and and employs the necessary strategy (like limp mode), and turns on the CEL. I've left sensors unplugged on vehicles and driven for many miles until I've gotten a CEL and limp mode if necessary. Doesn't really make sense to me, you'd think that an open circuit would be an instant CEL (sometimes it is), but I've seen otherwise in the field.

P0151B, P0171B, P0174B
Those are the three codes that's bad O2's right?

The P0151 is a code for the O2 sensor before the cat on bank 2 which is the passenger side.

The P0171 and P0174 if I remember just off the top of my head are both codes for an overly lean condition. You don't by any chance have any bad exhaust leaks right near the O2s before the cats do you?

+1, since you just had it apart, I'll bet that somewhere there is an exhaust leak giving the O2 sensors a bad reading. Did you remove them when you removed the y-pipe, and maybe not get one back in all of the way or something?