A very quick and free test is to undo the cat FOR ONLY THIS TEST!!!.
It sounds like a problem I had a couple of times with an older XJ I had.
It was a plugged cat. Never showed up on the CEL.

 

That's not a bad idea. I'll try unbolting the exhaust and see if that helps.

 

If the cat isn't the problem, I think I'd be doing a compression test.

 

although the crank position sensor is fairly new, I'm going to try that as well, but I don't think it's a mechanical engine issue. The oil and coolant looks great and the problem was intermettant for the past couple months.

 

Didn't get a chance to work on it since it rained all day. Any other opinions on what the check next?

 

Finally found the problem. Changed out the fuel pump unit AGAIN. Problem solved.... for now. Thanks for all the help.

 

Changed it out with...what? Did you use another cheap, aftermarket part? Didn't you mention earlier that you measured 43-50 psi. on the fuel pressure?

 

The first aftermarket one was bosch, which was crap anyways. This one was a used OEM unit that was in very good shape, and it fired right up and drove like a dream.

 

Bosch units come with a warranty. I install their oem replacement pumps on customer cars all the time without any comebacks, yet anyways.. How long did it last? Maybe a dirty tank/constantly driving on an empty tank is contributing to your premature pump failure trend?
Any thought as to why your pumps are failing??