GURPS High-Tech seems to have noticeable gaps in TL8 military gear. Fortunately, it appears to be possible to fill those gaps by extrapolating from what we do have. I've decided I'm going to try to do that here, starting with US Armed Forces equipment currently in service.
Existing coverage of small arms appears to be excellent.
High Tech already has stats for the M16A4, M4 Carbine, MK 17 Mod 0, M24, M107, Mk 14 EBR, M107, M870, M26 MASS, MP7A1, M240, M60, M249, M9, P226, and M1191.
Tactical Shooting has stats for the HK416, M110 SSAS, and M27.
One gap in the coverage, based on
this Wikipedia article, is a couple of "designated marksman rifles", but as far as I can tell those are basically just fine-quality (accurate) M16s*.
For anti-tank weapons, the Javelin, AT4, and M3 (Carl Gustaf) are covered. The
SMAW (Mk 153) is not covered, but it appears to be very similar to the Carl Gustaf. (This is the piece of extrapolation in this post I'm least certain of, so I welcome correction.)
Specific US mortars in active service aren't covered by
High-Tech, but as far as I can tell mortars haven't changed much since WWII, except for getting lighter. If it matters, I'd use weights taken from Wikipedia and combat performance from WWII-era mortars.
Vehicular machine guns and autocannons appear to be well-covered. Specifically, the M61, M134, M2 HMG, and Mk 19 grenade launcher are all accounted for.
So far, most of this has been just a preview. We'll have to do more extrapolating as we get further into vehicles.
Update: Edited to clarify the designated marksman rifles are fine (accurate). They may also be fine (reliable) but the main goal of their design appears to be accuracy.
*Update II: For reasons Icelander points out, at the level of granularity GURPS accounts for they may be essentially ordinary M16s.