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Those values correspond to settings for the two transmit gain stages of the MAX2829 transceiver. The amount of gain each provides is in the help docs for the tx_gain command. Those values come from the MAX2829 datasheet. Specifically,

(1) The first number (3 in your example), refers to the Tx baseband gain. See Table 17 on page 36 of the MAX2829 datasheet. The maximum value of 3 provides the most gain. A value of 2 provides 1.5dB less power than the max. A value of 1 provides 3dB less power than the max. Finally, a value of 0 produces 5dB less power than the maximum value of 3.

(2) The second number (30 in your example) refers to the Tx VGA gain. See Table 4 on page 14 of the MAX2829 datasheet. The maximum value of 63 provides the most gain. Each value less than that provides .5dB less transmit gain. Once you get down to a value of 47 and lower, you lose the .5dB resolution and instead drop the gain by 1dB every two steps. At its minimum value, the VGA gain provides 30dB less gain than the maximum value.