Before doing anything drastic, just jack up the rear, & disconect a shock at the bottom. Cycle the shock a few times over its full stroke. Once you are sure that ALL the air that might have been trapped has been bled out, then cycle the shock once more. You should have some resistance compressing it, but even more resistance extending it.

If they don't perform as they should, then i don't care what the brand is, or what the reputation is, stuffed shocks are stuffed shocks & if this is the case, then replacements are in order.
I think that 1200 coupe shocks have a slightly longer stroke, but fit & work anyway. This is what i was using in my 1k sedan for about 20 years. The shocks that i used were KYB Gas ones, & along with new bushes & slider blocks in the speings, this was all it needed for an acceptably good ride & good street handling. Mind you, all i had in front was an improved 1200GX engine with dogleg 5 speed, not a big output power plant by any stretch of the imagination.