In most cases with the TH400 not upshifting till really high RPM's is modulator related.
Even so there are two other players in that game, the governor and downshift solenoid.
I'm not sure why you have a bunch of debris filling/collapsing the governor screen, flag went up there when I saw that comment.
You also mentioned damaging the accumulator bore. Did you take the VB completely apart for some reason? That's risky business and can very quickly get one into big do-do as it only takes one valve in backwards or spring on the wrong side of a valve, or spring left out, etc to screw the pouch with that sort of thing.
I suppose replacing the VB is a good move at this point, hopefully it will cure the issues but if you've got a buttload of material moving thru the unit I suspect the problems may not be over.........
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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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