The stock indoor seems fine for local VHF but not too good on the 800 mhz
trunked system. How does the dicone work on the 800 mhz band?

Bob-

A basic discone has about a ten to one frequency range. The latest version of
Radio Shack's discone has a vertical element added so it can be used to
transmit on the Six Meter Ham Band. The earlier version without the vertical
element, was good from about 100 MHz to 1000 MHz.

The discone is intended for use with scanners. Even with the Six Meter
element, it is probably the best choice readily available to cover all
frequencies up to the 900 MHz Ham Band. You may be able to remove the element
and see if it makes any difference at the higher frequency.

73, Fred, K4DII