Hi all, I have a 97 f250hd with a 460 that has started shifting from 2nd to third at about 25-30 mph and lugging the engine. it usually will shift back and forth,but sometimes it stays it 3rd until i manually shift to 2nd.

I dumped some seafoam trans tune in yesterday and am going to change the fluid tomorrow. Is there anything else i should check? Any other ideas?

I'm off to orillies to get an OBD1 reader to check for codes, but there haven't been any lights come on on the dash.

Thanks