ive got a 383 (fresh rebuild 2000 mi ago)... this thing in second and third falls on its face at 4500 rpm??? its got a .486/288x .486/296 cam on a 106 center line its a 10.3:1 motor with 516 casting heads and yes i put the reacomended springs on the heads with proper shims... it has headman elite ceramic headers and dual 2.5 exhaust a 666 factory casting intake and 750 edie carb lower end was also balanced when rebuilt... i have now put msd 6al and a holley red fuel pump trying to fix this its gott be intake and carb right????
                                pullin my hair out
                                     marshall  

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Tell me what is your total timing and what rpm does it all come in.
Then check to see that you have full opening of your throttle blades with pedal to the floor[with someone helping of corse].
what gear are u running?
Have you checked for vacuum leaks.
Normally I see this happen due to a bad ign box or ground to it, but you've eliminated that with the MSD or the throttle not open all the way.
The intake does you no good but would not allow it to rev good in 1st then fall out in 2nd, 3rd.
Just curious, what are your spring pressures at installed & open? and does it do it with the engine only somewhat warmed up?[enough to drive] that is.
I'm going to work for a few hrs, later.  

ok total time is 38 degrees it all comes in bout 3500
i do have full blade opening i am runing a set of richmond 3:55 sure grip and i baught a 800 cfm holley and an edelbrock tm6 in the last two days i havent putem on yet, it does it at all temps and as for spring presures i am not sure but i had the best machine shop(on reputation and by far the highest price) in my area do the whole motor and set it all up i have all factory rockers should i change
                             thanks
                               marshall  

So what do the plugs look like?  

tanish  

Hows your gas has the car been sitting?
Otherwise sounds a lil rich and if your in the west you know you just can't hardly color a plug with today's gas and would have to be 'fat' to see a decent amount of color on the plug at all.
What kind of cylinder pressure do you have?  

Put the new carb on, I suspect the back half of your carb is not working properly. I have seen absolutly the same problem, no fuel getting through the back half of the carb. My own holley would fall on its face right a 4500 rpm until I corrected the problem.  
There was a blockage in a brand new holley hp main body from the rear accel. pump, I drilled out the blockage and the problem was solved.  

When You say "falls on it's face" I assume you mean out of the hole it's great but when you get to 4500 rpm it stumbles?  Sounds like a fuel starvation problem to me.  Assume nothing.  Check the specs on your fuel pump.  Pressure AND volume. It's possible you got a Chinese made POS from Holley. How old are your fuel lines?  Sometimes there is a rubber "flapper" inside it stays flat until a certain flow at which point it'll flap up inside the hose/line and cause a blockage.  What diameter hard steel line are you using, anything less than 3/8" is no for your combo. Healthy 383's love to drink. Check bowl float levels.  Maybe the thing is running so great that it's emptying the bowls. 1/32 of and inch makes a huge difference on set hight.  The beautiful thing about the 383 is that it's totally old school.  Remember fuel fire and air that's all it needs in the right mixture and it'll run like ........a bat out of hell.  Check to see if any Toyota's or Datsun's are stuck in the air cleaner.  ha ha   hope this helps