As Trev29 says, the ignition timing may be off. Also timing -related is the Volvo/Chrysler Ignition CU used on 82-88 240s, which is believed by some people to affect NOx production. If timing checks out OK, you could try removing and plugging the vacuum line to the ICU (below the windshield washer tank).
What follows is a "canned response" I post on the subject. I have more back-up detail if you want.

"NOx and Volvo/Chrysler Ignition"
You have the Volvo/Chrysler ignition used on 240s from mid '81thru 1988. It's been claimed that the V/C ICU's design can cause hi NOx, and that plugging the vacuum line to the ICU can lower NOx production with little effect on normal operation.

I first posted it on 5/21/04 (see original post here. ) At least one person has found that this solved his high NOX problem.
You can see his happy response at success story.

NOTE that he had failed with a new cat, then plugged the ICU vacuum, put the old cat back on and passed!.

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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

"My car crawls to 20 MPH going uphill and overheats."
"the car lacks power and "pings" on acceleration. "
My guess is that your timing is too far advanced. Advanced timing leads to high engine temps, (and detonation/pre-ignition/pinging) resulting in high NOx.

Back off on the gas when you get pinging else you are likely to blow a hole in your piston(s).

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1980 245 Canadian B21A with SU carb and M46 trans