Huge Problem 77 Cutlass Salon, Driving Issue

It has a 350 Rocket in it, with a 4 week old Eledebrock Carb, and intake. During the 4 week period of having it on. It Ran like a champ, but now for some reason. It runs good for 15-20 minutes, but after it reach normal operating temperature,. It starts running like a tired dog. Only goes 10-15mphs, What could cause something like that? Bad Coil in the distrubutor? New spark plugs and wires, Rotor Button and cap 2 months old.

No power at full throttle, misfires, loads up and smokes, what specifically do you mean, we need a more comprehensive description of what is occurring here. What other changes/mods have been done?

No power at full throttle at all, seems to bog down, and will not pull any hill at all.The car isn't overheating though. No water in the oil or coming out the tail pipe.No misfiring, but the car is idling kinda crazy. Up and down.

No power at full throttle at all, seems to bog down, and will not pull any hill at all.The car isn't overheating though. No water in the oil or coming out the tail pipe.No misfiring, but the car is idling kinda crazy. Up and down.
Check for a blocked cat, drop the exhaust down just for a test and see what happens. Remember there is a fuel filter in the tank, ever been changed?

Never changed that filter, but it has a Holley Fuel pump, and 1 of those class filters right before the fuel lines goes to the Carb. So, it's getting plenty of gas. It's always full. Just when the car heats up to normal temp. It runs like a tired dog. It will only do 10-15 mph. Any type of help to point me in the direction would be, well appreciated, and thank you. The Car has custom exhaust, no Cat, straight pipes to each manifold, with flow master muffler.

[Problem really didn't start until, my step dad let a community patient "Methane Head", install 2 new lifters on the passenger side head, while i was at work. 2 weeks after that the car started cutting off and bogging out. I looked under the hood not 1 intake bolt was tighten and you could see where water was running down the front of the engine. I replaced the intake gasket and tighten it back down propertly, but the car stopped cutting off, but didn't stop bogging down.]