Test I thought of...
try jumpering the radiator fans to go high speed, leave the AC off...
does it stall coming back to idle?
AC compressor puts a big load on the engine, but AC on means fans go on high speed which puts a big load of its own thru the alternator. Mike mentioned the Voltage Regulator could be sketchy which could make the alternator act like a brake when 40 amps of rad fans turn on
