First things first. Mechanics are not necessarily in the same union as the drivers. Often, the mechanics are IAM (machinists) as opposed to Teamsters. However, in an odd twist, as of 2014; I believe pretty much all IAM mechanics were switched over to 'Teamcare' (a Teamsters H&W plan). Overall, low copays/out-of-pocket (much better if you are near larger metropolitan areas with good access to certain 'preferred providers' for things like xrays/MRIs/lab work). I'm guessing you would be in TeamCare.
Unfortunately, some searching on here might reveal much discontent with Teamcare. Basically what happened was those who were in the company's plan previously, suffered a slight decline in their benefits by moving into Teamcare. On the plus side, those who were already in TeamCare ended up with a slight improvement in their coverage.
Medical/Dental, I'm sure you would be satisfied. Vision? Meh. I'm not sure there is such a thing as really good vision coverage anymore.