If you "let yellow mellow" the poop hole in your toilet may be calcified with piss crystals and causing a coronary. I replaced my toilet with similar issues and was shocked at how small the discharge was. We were shitting through the eye of a needle!
LPT: For calcium buildup, turn off the water, flush, them pour lots of vinegar through the overflow pipe - which goes through the siphon jet into the bowl. The vinegar will dissolve buildup. Let sit for hours. CLR will probably work too.