you do not mention what fan or shroud you are using.

I agree, if it can keep up in town, air restrictions are hurting you on the freeway.

The fact it is coming back down at 55 tells me you have enough radiator and it is spending enough time there.

Something is blocking air flow.

It might still be possible that your lower hose is collapsing, and you could test that by staying in a lower gear at 55 so your rpm is higher.
if it starts creeping up, then I would use the steel hose with the rubber ends.
http://www.jegs.com/i/JEGS/555/511241/10...DYaAl-yEALw_wcB