225 Dart chugging past 70...

my MAzda pickup did just what you explained, same bad plastic filter but mine was right in front of the tank, would idle all day but once you got on it, it would bog bad. Changed filter and bingo, until I got it on the smog check dyno and it wouid start to drop RPM's on the dyno wheels. Weak fuel pump! all fixed now. Do yourself a favor and change out the headpipe on that 6. The pipe after the manifold to the muffler necks down to about 1.5 inches at the nasty production line weld, get a muffler shop to replace it with a mandrel 2.25, ala Super six. itll really uncork that 6.