The engine knocking is a concern and probably the cause. If the engine knock(ed) with little load on it and doesn't upshift it can't send the signal for the trans to behave and upshift on time or go in to overdrive. The engine needs to be looked into. Doesn't this have a timing belt? How many miles and how many times has it been done?
Even with care, time and miles take a toll. I have to remind myself of that as I care for my own vehicles and do over-expect idefinate life out of them and get away with it pretty good. It's time for a go thru on the things you just can't stop from aging,
T
Tom Greenleaf - MetroWest Boston - USA
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http://www.autoacsystems.com/tomgreenleaf/