[Amps] How to improve efficiency

[Ve6wz_Steve]

I have a HB 4-1000 amp, GG, 6 kv on the anode, tuned input, PI output.

Output (and input) is awesome on 40m, but I cant get the same steam on
80m.
I realize that efficiency can be variable from band to band, but what
can be done to improve single band (80m)performance ??
Where do I start ?  I presume changes to the tank circuit may be in
order??
I DO have sufficient loading capacitor range.
Any suggestions.

de steve ve6wz.