The camshaft was replaced at 133,000 miles is this a red flag?

The 3.6 is known for having camshaft issues. What normally happens is that the roller on the rocker arm fails and then it starts grinding on the cam lobe. If you catch it very early when it is barely ticking, you can usually replace just the rocker arms, and it will be fine for another 100K or so. If however, you wait until it really starts really rattling it is commonly too late and now it needs a new cam, and all the rockers replaced. There are at least 4 generations of them with continued "improvements" to the cams in each version. Unfortunately, they haven't yet solved the issue, so this is still a common failure.
If it were me, I'd have a shop you trust, look it over and see what they find. They are known for the engine, and frame issues as well as the oil cooler leaking so the top of the engine has to come apart to replace the seals. If that was done when it was apart for the cam (and if they replaced the rockers and cams on both sides) it might be okay.