A TH350 determines its light-throttle shift point largely from engine vacuum. Higher vacuum (low throttle) = lower rpm shift, lower vacuum (more throttle) = higher rpm shift.
If it's shifting higher and harder than before (you didn't say, exactly), I would look to see that you didn't bump or damage the vacuum hose that goes to the vacuum modulator on the transmission. If it's disconnected, the trans won't see any vacuum and will think you're at wide open throttle = late & hard shifts.