Gas Is Drowning Me!!!

ok I am getting TERRIBLE mileage on my truck recently. I used to get around maybe 11ish mpg, but now its seriously around 2-3mpg. My cat was clogged so I put in a straight pipe, but it only started running rich and just drinking the stuff like a few weeks afterwards so i dont think thats the problem. I've spent a little over $70 on gas this week just to get to school, then shop class, then home. I've replaced my wires, cleaned and gapped plugs, new cap and rotor, took out clogged cat, and changed the oil and oil filter. It bogs more than a fat lady running to the pisser when im at idle or stoped too, but its done that since i got it about a year ago, but its getting worse as the days go by i can tell. I cant go more than 1/4 throttle in first gear no matter what gear I put it in. I have to feather it to about 1/4 throttle to even get moving decently. When I WOT it in first (idle or stopped pretty much) the engine tone gets deeper and sounds like it has a hard time speeding up to the rpm it should be at, but after about 7 seconds it kicks up and is fine there on. The exhaust tone also gets really deep, and has a very spaced out hollowed clapping sound. Like a half second delay inbetween claps. Dunno...just sounds like it bogs down really bad cant explain it well. Any help would be awesome about the gas problem, and the bad running in first gear, or at slow speeds or whatever. Thanks.

O2 sensor maybe?

I think you have another thread on this.

However, if an engine bogs on full delivery, it can be only two things. Ignition or fuel. You might laugh at that BUT, the key is to look at the basics first.
1. Ignition timing and check for advance. On an '89, disconnect the ECM wire and check your base timing. Reconnect the wire and see that it is advancing at idle.
2. If the above is OK, Check fuel pressure, with a guage. If it is not, try replacing the fuel filter and recheck.
3. If 2 is OK, check the vacuum. It should be about 18-19 in/hg. If it is not, there is a leak. Start checking your hoses. If their OK, take a can of WD-40 and spray the base of the TB and around the intake to head. Your looking for a bad gasket. If it is bad, the RPM will go up.

These are some basic points to start with.

Yeah I think there is like one other one, but they are about different things about the same subject kinda. Anyways the vacuum test i did was fine 17psi at idle and all the rest was fine. I replaced the fuel filter, oil filter and oil just a bit ago...I know the timing is off a bit but why would it get worse gradually over time like this? just cuz of the timing? Thanks