The errata is being compiled, but it is written.
Basically you calculate the TMM for the ground movement, then calculate the TMM based on the jump (or submersible) movmemet (without the +1 for jumping.
If they are the same (8” ground with 6” jump, both are +1 TMM), no special.
If jump TMM is higher (from improved jump jets, partial wing, etc) it gets strong jump jets equal to the difference.
If jump TMM is lower (shadow hawks with 6” jump and 10” ground), it gets weak jump jets equal to the difference.