'93 Vic tranny

Recently, while accelerating from stop, the transmission seems to shift "early" from 2nd to 3rd and from 4th to 5th (overdrive?) causing the engine to bog down. Also it shifts back into 4th after reaching cruising speed and stays there unless you punch it. The engine never stalls out and always starts on the first try. I replaced a cracked fly wheel about 6 months ago and replaced all the fluid and filter at that time. The fluid level is still full and clear with no burnt smell from it. All gears work fine from a dead stop, (2,3,D, reverse). Any ideas???:cya: