So after replacing the spark plugs, distributor cap and rotor, my 81gl sedan runs a million times better ( who would have thought? ) but now even after its warmed up once i reach 4k it sputters and hesitates like almost as if their is a lack of fuel. Any ideas on what that could be? Also I pretty sure i have a blown headgasket or a cracked head... as a short term remedy would that BlueDevil sealant be a good choice? Thanks for the help! heres a pic just because

Can't comment on Blue Devils...but have you changed the fuel filter?  Fuel pump delivery checked?

If you have a bad head or gasket, just fix it. In my opinion NEVER use Blue Devil or or other chemical head gasket sealants.

I can validly say that Blue Devil works. I had to use it right before WCSS because the HG's popped on my EA82T and I didn't have the time or money to do a HG job.

 

As for the lack of power above 4K, is your ignition timing dead on?

As was mentioned, check your fuel filter. Make sure that's not clogged or slow flowing.

Check the lash on your throttle cable, Make sure you're getting full throw out of the throttle shaft.

Have you run any seafoam through the fuel system? You may have some crud or varnish in the carb.

Do you have any valve tick? Do you have proper oil pressure? Improper oil pressure can cause a tick and make hydraulic lifters fail to fully inflate. That will limit your power.

 

Twitch

Distributor might be badly worn, and/or the mechanical advance might not be functioning properly.

pluged rear feul fillter or iceing up carb

Differential diagnosis between fuel flow and electrical is whether the break-up always occurs above a certain RPM range (even with light throttle) or whether it occurs at lower RPM with heavier throttle (more load, more fuel needed).

Make sure you adjust your valve lash too.  A lot of people don't ever maintain it, and eventually it will get far enough out of spec that it will do weird things to the performance of the engine.

Thanks for the input guys, im thinking its the fuel filter and or pump.... as of last night and this morning it is starting EXTREMELY cold, to the point where giving it gas does almost nothing and it dies almost immediately. I have to keep the key in the ignition turned a hair to the right while giving it a little gas to keep it from dieing while it warms up. and now instead of sputtering over 3-4k it sputters and jumps coinstantly for the first ten minutes of driving and then eventually goes back to the only over 3-4k.... but the weird part is that it doesnt do this all the time.... like some days it will run and drive without any antics and some days its almost impossible to drive.

Thanks for the input guys, im thinking its the fuel filter and or pump.... as of last night and this morning it is starting EXTREMELY cold, to the point where giving it gas does almost nothing and it dies almost immediately. I have to keep the key in the ignition turned a hair to the right while giving it a little gas to keep it from dieing while it warms up. and now instead of sputtering over 3-4k it sputters and jumps coinstantly for the first ten minutes of driving and then eventually goes back to the only over 3-4k.... but the weird part is that it doesnt do this all the time.... like some days it will run and drive without any antics and some days its almost impossible to drive.

The fact that you have to hold the key a certain way to keep it running, and that the problem is intermittent suggests that the switch or wiring between the switch and the coil is bad..  Try jumping the batt + to coil + with a jumper wire to see if the symptom improves.