My 327 Chevy engine was running well, but I noticed that the fuel pump had a
small leak, so I installed a new fuel pump. After installing the fuel pump
and cranking her up, the motor was shuddering like crazy, but then smoothed
out, however the shuddering resumed as soon as I put it in a foward gear. I
reinstalled the old pump but the engine is still shuddering. The wierd
thing about this problem is that the engine will idle fine and will move in
reverse gear with no problem, but as soon as I put it in a foward gear, it
shudders and stumbles wildly. If I put it back in neutral it idles fine, and
I can rev the engine way up without any problem.

So far I have installed a carb kit (Edelbrock 600) and installed new spark
plugs but still have the exact same stumbling and stalling problem when
foward gear is engaged. This thing has me mystified and I really would
appreciate any ideas anyone might have as to the possible source of this
problem. (Tranny is a 350TH).

Thanks in advance for any advice.