Regarding the 5.3L Jasper reman, you may want to reconsider the use of T6.
Jasper's warranty (3yr/100k miles; a very good one) is predicated on using OEM fluid/filter recommendations (as are most all reman and aftermarket entities).
You would be jeopardizing your new engine warranty if you use T6.
http://qms.jasperengines.com/warranty.asp
"Buyer specifically acknowledges that proper maintenance procedures which include, but are not limited to, changing or calibrating, as applicable, the filter, lubricant, ... must be performed as recommended by the original manufacturer or the warranty will be void." (underline my emphasis)
You might want to email them and get Jasper's acknowledgement in writing if you intend to use a lube grade not spec'd for the Vortec engine by GM.
Additionally, while it is admittedly very unlikely that Shell T6 would cause any issues in your other two cars, it's also very unlikely that Shell would be willing to extend any warranty coverage for the use of T6 in your other vehicles. This is because Shell, and just about any lube/filter maker I can think of, predicates their warranty coverage to those that mimic the OEM application recommendations. Just because you like T6 in your cars, does not mean Shell will be required to cover any damage (however unlikely) from the use of their lube in your application. If you use 5w-40 where a 5w30 is spec'd, that gives them the ability to deny, or at the very least, delay with great fervor, any warranty claim. Just because lube makers spec some of their diesel oils for gas applications, does not automatically mean they will cover YOUR SPECIFIC APPLICATION, should you choose to use a grade not covered by the OEM spec in your engine.
https://rotella.shell.com/warranty/terms-and-conditions.html
You might want to write an email to Shell and ask their position here as well.
I realize it's popular to go off the reservation and try new things; I do it often myself. But I do so knowing the risks I take, and how that affects my warranty coverage in the equipment and products I utilize. This topic is no different for lubes than filters. So many want to "upsize" their filter for some imagined benefit, where no tangible evidence shows any credible gain, and to boot, they risk the filter maker's denial of warranty coverage for choosing a filter not spec'd for the application. When an OEM specs/licenses something, the aftermarket often will use that same spec as their "recommendation" or requirement for their products as well.
Up to you; Caveat Emptor.
