"How" in what respects?

I-40 between OKC and the NM state line is 70 mph, pretty much straight and relatively featureless. Between the NM line and ABQ it's 75 mph, and becomes more hilly. I-25 from ABQ to Las Cruces is 75 mph and somewhat hilly. None of it is a difficult drive unless you hit an ice or snow storm, which is highly unlikely in April. High winds are always possible, like anywhere else out that way.

Suggestion - if you are going to be in Amarillo around dinnertime, have a steak dinner at the Big Texan (the ribeye is outstanding) and consider spending the night in their motel. It's more expensive than the Motel 6 but it's all done up inside and out in an Old West decor. No wifi in the rooms but there's free wifi in the restaurant, you can usually connect sitting outside.

Tolls: I-44 between the MO line and Tulsa is $4 and between Tulsa and OKC is another $4, there will be manned booths. Your EZ-Pass does NOT work in OK. If you plan on taking the toll road bypasses around Tulsa and OKC, you may need exact change, bring a roll of quarters. The booths are not always manned, and the change machines at the booths frequently do not work. Unless there's construction and/or you hit at rush hour, there's usually no problem with taking the freeways right through both cities.