missing/losing power

[Gordon Bird <gb@the-bdc.com>]

Had the A out last night, after normal valve/points adjust, etc,etc.  Fine
until warmed up (@190F), then at @ 5000 rpm's I get a miss and loss of
power.  Pulls just fine up to that point.  When cold, pulls strong up to red
line, when I quit.  I know Barney, it should be able to go higher. ;^)  
Any clues?
TIA
Gordie Bird
62 MGA
80 MGB
86 Audi 4kq