My car wobbles at high speed...?

The tires could be mounted improperly.

Probably a balancing issue with the tires. Never use different tires as it's unsafe to do so.

Solution is simple: get 4 new (all the same size & type) tires.

have your wheel balance checked and your alignment checked. you can't put two different size

tires on the same axel. as long as you have the same size tire on each end of the axel it's ok.

have your shocks and struts checked.

With a Ford Explorer it is important that all your tires are the same size. But im guessing the problem is with your wheel balancing. Get all 4 wheels balanced

A steering wobble indicates either a wheel is out of true (buckled) or a wheel alignment is required. I would bet on the latter. The three different tyres is not necessarily an issue if they are similar types and wear, though you may want to put the matched pair on the front. Worn suspension doesn't usually result in wobbles on the highway. You generally feel/hear it when you're cornering or riding bumps.You can quickly check the dampers for oil leaks by eye. They will have fresh oil visible or a whole load of dirt stuck to them if they've been leaking a while. Dampers/springs do wear and fade over time and you can swap them out if you want, but I don't think they're the problem.

You have three different tires?

No no no no NO. Do not do that.

"Now I have like 3 different tires in it".

Yup, that would be an obvious culprit, Alex. That and/or they are simply out of balance. When is the last time you have had all four wheels/tire balanced? It's worth the tiny bit of cash needed to do so if you want to eliminate the wobble.

Spend some money and put a new set of tires and get them all balanced.

Sounds like your wheels need balancing.

Take it to a mechanic. One time I had a wobble and mechanic found a weak spot on one tire that would bubble out at high speeds. He said I was lucky I didn’t get a blowout.