One thing to consider carefully is the BCR(Benefit-to -Cost Ratio) . IIRC, I got the 342 gears installed @2006, and
due to the fact I wasn't constantly hauling a lot of weight, started saving 3 MPG, over the original 410 gears.
It cost @ 2000$ back then, but in over 10 years I'd say I've easily gotten my money back in gas savings.
2000$ divided by 12 years =@167$ a year, and for highway travel these 342s have been the ticket.

But, IMO, if you're needing a gear change that badly, skip a ratio. The overall difference from 410 to 373,
or 373 to 342 just isn't advantageous enough, mechanically, to merit the considerable cost. The original
reason I got out of the 410 gears was the engine revs in overdrive, on the highway were almost insanely
high, around 3300 RPM, with no load, at highway cruising speed. I decided the low end torque advantage
of the 410 simply wasn't worth what I lost in gas mileage on the top end.