Transmision Problems need some help.

[sbbriderz]

I replaced my stock headers on my 68 with a 302/4brl with new longtube Hooker headers.
I have open headers on now and ready for exhaust but now transmission won't shift up. P,R, N, D work but it never shifts into second gear, 1st gear has no power while going up the driveway. Replaced with a new modulator.
The tranmission worked perfectly fine before installing the headers.

New Modulator
no bent lines
fluid level as needed

any advise?

[JV106]

No idea on why it won't shift, but not having back pressure will kill a ton of its power.

[garycrist]

You sure the kick down rod is not hitting and/or connected?

[S_K]

Did you loosen the bolts on the transmission by any chance? Torque converter moved forward slightly? I am assuming it is a C4?

[sbbriderz]

Nothing on the trans was messed with before of after the headers.
I just replaced the filter and gasket on a final hope that the filter needed to be replaced. The engine appears to be idleling at higher rpms while on park and pulld hard when taken into drive. You guys think installing the exhaust might fix it? maybe losing compression somewhere?

[S_K]

I doubt it. Exhaust will change performance some, but not that much.