'95 Pontiac Sunfire won't shift into 2nd without lifting off the gas?

1995 Pontiac Sunfire 2.2l 3-speed shifts fine at first when cold. When the engine reaches normal operating temp, it will not shift into second without letting off the gas. Car has 229k miles on it and runs fine dispite this. I've changed the filter and fluid, checked the detent cable and changed the trans control solenoid. Ideas?