01 neon hwy overheating? Help!

I just bought a 2001 neon 2.0 automatic,the problem is it only overheats when your driving it at hwy speeds, I can drive it around anywhere in town and it doesn't overheat but when I get it out on the road say around 45-55 it starts to overheat fast.
I'm an old school mechanic pre 1990 but have a terrible time with this neon

things I've checked or done

changed thermostat
ckecked for good water circulation ( good)
pulled the cat of and it looks to be almost new! not clogged at all (maybe someone had the same prob)
good even compression
no water in oil

this thing has got me puzzled

something else I noticed the harmonic balancer is wobbly and needs rreplaced.

last minute thought! ( vaper lock in the cooling or collapsing hose? )
any ideas ?
thanks, Allen

Are you running your engine with anti-freeze?, because on vehicles that had run with water, and its rusty, rust tends to eat the little blades on the water pump, and if you check your car at idle it assumes to be working right, but when it works under pressure it tends to fail, because these blades are either worn out or doesnt exist anymore, also if you dont take care of this your engine head can get damaged too.

Radiator may be plugged. When idling at full operating temp, try to check the radiator (CAREFULLY!!!) to see if there are cool parts. If there are, there is a blockage in the radiator.

Check your 'radiator cap'. It's no longer on the radiator for Neon, but it looks the same. If it is not sealing well, your system is operating less than optimally.

Are hoses old? They could be collapsing due to fatigue, especially when running at higher speeds.

May seem silly, but check to see if anything is blocking the front of the radiator when you get to highway speeds. If air flow through the radiator is blocked, the coolant cannot get cooled, and will get hot fast.

i had a similar problem found out it was the wires for the radiator fan. the connector had gotten loose due to being able to move around. just taped it together and poof no problem. try checking the wires out.