Are you sure? It causing different epoch. Also on ETC GPU clock is 2100MHz and MCU 40% usage. On ETH GPU clock is 1500MHz MCU 100% usage. Totaly real usage during mining.
ETC-mtweak 1
20201121 07:32:17 Mining at ethash.mine.zergpool.com:9999
20201121 07:32:17 GPU #1: EVGA GTX 1080 Ti - 18.20 MH/s, [T:49C, P:144W, F:55%, E:128kH/W], 2/2 R:0%
20201121 07:32:17 GPU #3: EVGA GTX 1080 Ti - 18.33 MH/s, [T:51C, P:146W, F:55%, E:127kH/W], 2/2 R:0%
20201121 07:32:17 Shares/min: 4.048 (Avr. 1.524), Avr.Power: 286W, Avr.Efficiency: 128kH/W
20201121 07:32:17 Uptime: 2 mins 37 secs | Algo: ethash | T-Rex v0.18.11
ETH-mtweak 1
20201121 07:33:52 Mining at ethash.mine.zergpool.com:9999
20201121 07:33:52 GPU #1: EVGA GTX 1080 Ti - 42.85 MH/s, [T:46C, P:146W, F:54%, E:330kH/W], 1/1 R:0%
20201121 07:33:52 GPU #3: EVGA GTX 1080 Ti - 42.14 MH/s, [T:47C, P:143W, F:55%, E:329kH/W], 3/3 R:0%
20201121 07:33:52 Shares/min: 23.706 (Avr. 5.614), Avr.Power: 258W, Avr.Efficiency: 329kH/W
20201121 07:33:52 Uptime: 42 secs | Algo: ethash | T-Rex v0.18.11
Wow, that difference in hashrate can't be explained by a not functioning memory tweak. "--mt" is only supposed to boost your hashrate by a couple of MH/s per card, there's definitely something else going on. I've seen similar reports elsewhere it's a common problem regardless of what miner is used. I'm not aware of a solution for this issue, unfortunately.