He suggested buying a new driveshaft to cure angry sparrows?!? Yeah, spend $300 on a new shaft instead of $90 for a new CV and u-joints.
And a stock driveshaft is fine length wise on a 4" lift, (like stated though) long travel shocks cause an issue.
10" travel shocks not just long travel, on the front of a tj will bottom out the slip joints and use the t-case as a bumpstop. Some 2.5" and 3.5" lifts run 10" travel shocks.
The mechanic, was not wrong, it is too long for the current application.
Some of us choose to run them anyway. When the OP decides to jump his jeep or accidently takes a woop to fast, the OP could likely be replacing a t-case instead of a couple u-joints.
When a shaft is too long, shorten it. The cost is minimal compared to a shaft that is too short or buying all new joint and cv's unless they are toast anyhow, or replacing the joints and buying a long arm upgrade to avoid a correct length shaft to run on the current short arms... or buy a set of shorter shocks.
Shops are not open to help the do-it-yourself crowd. They are there to make money so the doors can stay open. When I myself can get away with selling parts instead of spending hours I can't legitimately charge for pollishing a turd, I do so.
Occasionally, I will screw up a seal putting together a spicer joint. Guess who gets to buy the second one?... ya, me, what might happen if I knowngly install a shaft that is too long and the rig comes back with a busted t-case?
BTW, I have a 241 case that is busted, wonder how that happend?