cursed buick

Hi, my name is tony, Im new to this sight please be kind.
I have a 1991 Buick century I have changed all the cooling system parts from radiator to waterpump,thinking the problem was,its getting to hot because it presents the same symptoms,skipping, loseing power backfiring
I checked the compression on all cylinders all were over 180 so I figured its not a blown gasket but its still doing the same thing,I also checked fuel injectors all seem to be working
please does anyone have any ideas? 3.3 Ltr eng,61000 mi.,6 cyl, auto trans

Coil output check and backpressure test.....

Last COMPLETE tuneup?

Check for codes?

Check for vac leaks?

Last tune up about 5 mnth
Compression chack ok
Havnt checked vacuum yet cant figure how