I had an LT4 in a MY16 Corvette Z06/Z07 and while I loved a lot about it, the one thing that could be improved was in its intercooler and charge air cooling. GM addressed the intercooler in MY17 but the CAC circuit was always limited in its ability to adequately cool the vehicle. GM ultimately addressed this issue with the LT5 in MY19 on the ZR1, with a taller and larger blower along with two chin-mounted radiators for the CAC circuit.
If GM wants to do anything serious above the ZR2 they need to skip the LT4 and do the LT5. Of course, GM dealers would attempt to charge out the wazoo over and above MSRP for it, and with new auto interest rates in the 7's and above now, dealers are going to have to start selling much less than MSRP in order to survive.
I don't really need any bigger tires than I already have on the ZR2, the GY Territory MT's are an interesting choice (apparently less expensive than the Duratracs at D/T,) and work just fine for me. The 3.23 doesn't bother me too much with the L87 because for maybe one or two-tenths in the quarter mile as it is, I'd rather have the extra 1 or 1.5 mpg. The TRX is cool but its big block fuel economy would get old quick. I'm still getting used to the ZR2's mid-teens coming from a diesel-powered Land Rover. I do like the L87 but I probably would have went with the LZ0 had it been available in the ZR2. Apparently, the AT4x uses the same front end as the AT4, so there is no reason why it shouldn't be able to be optioned with the diesel.