Just drove my new wagon home from Tyler last night. It has the 235 with powerglide. Was cruising 55mph on the straights, but when I hit any incline... it would drop to 30- 35 and continue going down. Was told it sounded like no compression- ring issues... does this sound accurate? Is this a simple easy fix- or is it going to be extensive and pricey? All is original- still 6v.