1998 Bonneville loss of power when turning

1998 Bonneville SLE looses power when turning particularly while engine is warming up. Fresh tune up, wires, fuel filter, air filter, etc. I am told that the pressure in the fuel lines are normal and there are no leaks. Has has this problem for a long time, tune up etc. did not cure. Once car is warmed up problem goes away. Miles 84K. Seems to be absolutely fuel related.