Unable to get a consistent GPU performance on GTX770

Hi
I encountered some serious lag spike recently, and I find out the reason: my GPU can't hold 100% usage duringthe BF4 game ply, the GPU load frequently drop to about 20%.
I am running the game on a 4K screen and using the other 2K screen to show the battle map on battlelog. (BF4 gameplay)

The following is the GPU-Z LOG. I bolded the GPU load.


Date , GPU Core Clock , GPU Memory Clock , GPU Temperature , Fan Speed (%) , Fan Speed (RPM) , Memory Used , GPU Load , Memory Controller Load , Video Engine Load , Power Consumption , PerfCap Reason , VDDC ,
2015-03-15 02:59:59 , 1228.1 , 1752.8 , 60.0 , 71 , 2340 , 1915 , 99 , 58 , 0 , 91.7 , 4 , 1.2000 ,

2015-03-15 03:00:00 , 1228.1 , 1752.8 , 62.0 , 85 , 2310 , 1913 , 99 , 56 , 0 , 94.1 , 4 , 1.2000 ,

2015-03-15 03:00:01 , 1228.1 , 1752.8 , 63.0 , 85 , 2340 , 1913 , 99 , 57 , 0 , 94.1 , 4 , 1.2000 ,

2015-03-15 03:00:02 , 1228.1 , 1752.8 , 64.0 , 85 , 2430 , 1913 , 99 , 54 , 0 , 93.6 , 4 , 1.2000 ,

2015-03-15 03:00:03 , 1228.1 , 1752.8 , 64.0 , 85 , 2490 , 1915 , 99 , 56 , 0 , 93.6 , 4 , 1.2000 ,

2015-03-15 03:00:04 , 1228.1 , 1752.8 , 65.0 , 85 , 2610 , 1916 , 98 , 59 , 0 , 92.6 , 4 , 1.2000 ,

2015-03-15 03:00:05 , 1228.1 , 1752.8 , 65.0 , 87 , 2640 , 1912 , 99 , 59 , 0 , 93.3 , 4 , 1.2000 ,

2015-03-15 03:00:06 , 1228.1 , 1752.8 , 65.0 , 87 , 2670 , 1920 , 99 , 59 , 0 , 92.1 , 4 , 1.2000 ,

2015-03-15 03:00:07 , 1228.1 , 1752.8 , 65.0 , 87 , 2730 , 1930 , 99 , 58 , 0 , 92.9 , 4 , 1.2000 ,

2015-03-15 03:00:08 , 1228.1 , 1752.8 , 59.0 , 87 , 2760 , 1938 , 19 , 13 , 0 , 50.6 , 4 , 1.2000 ,

2015-03-15 03:00:09 , 1228.1 , 1752.8 , 56.0 , 87 , 2790 , 1935 , 18 , 13 , 0 , 43.9 , 4 , 1.2000 ,

2015-03-15 03:00:10 , 1228.1 , 1752.8 , 55.0 , 80 , 2790 , 1932 , 13 , 9 , 0 , 40.9 , 4 , 1.2000 ,

2015-03-15 03:00:11 , 1228.1 , 1752.8 , 56.0 , 80 , 2850 , 1930 , 20 , 13 , 0 , 46.0 , 4 , 1.2000 ,

2015-03-15 03:00:12 , 1228.1 , 1752.8 , 54.0 , 80 , 2790 , 1929 , 25 , 17 , 0 , 44.2 , 4 , 1.2000 ,

2015-03-15 03:00:13 , 1228.1 , 1752.8 , 54.0 , 80 , 2760 , 1929 , 12 , 8 , 0 , 40.0 , 4 , 1.2000 ,

2015-03-15 03:00:14 , 1228.1 , 1752.8 , 54.0 , 80 , 2730 , 1928 , 13 , 9 , 0 , 40.4 , 4 , 1.2000 ,

2015-03-15 03:00:15 , 1228.1 , 1752.8 , 53.0 , 79 , 2730 , 1927 , 17 , 12 , 0 , 40.8 , 4 , 1.2000 ,

2015-03-15 03:00:16 , 1228.1 , 1752.8 , 54.0 , 79 , 2700 , 1927 , 14 , 9 , 0 , 47.4 , 4 , 1.2000 ,

2015-03-15 03:00:17 , 1228.1 , 1752.8 , 53.0 , 79 , 2700 , 1926 , 24 , 16 , 0 , 40.7 , 4 , 1.2000 ,

2015-03-15 03:00:18 , 1228.1 , 1752.8 , 53.0 , 79 , 2640 , 1924 , 11 , 8 , 0 , 39.7 , 4 , 1.2000 ,

2015-03-15 03:00:19 , 1228.1 , 1752.8 , 53.0 , 79 , 2670 , 1924 , 12 , 9 , 0 , 38.8 , 4 , 1.2000 ,

2015-03-15 03:00:20 , 1228.1 , 1752.8 , 53.0 , 78 , 2610 , 1924 , 13 , 9 , 0 , 40.5 , 4 , 1.2000 ,

2015-03-15 03:00:21 , 1228.1 , 1752.8 , 52.0 , 78 , 2640 , 1924 , 12 , 8 , 0 , 41.2 , 4 , 1.2000 ,

2015-03-15 03:00:22 , 1228.1 , 1752.8 , 53.0 , 78 , 2610 , 1923 , 25 , 17 , 0 , 45.1 , 4 , 1.2000 ,

2015-03-15 03:00:23 , 1228.1 , 1752.8 , 53.0 , 78 , 2610 , 1923 , 25 , 17 , 0 , 43.5 , 4 , 1.2000 ,

2015-03-15 03:00:24 , 1228.1 , 1752.8 , 52.0 , 78 , 2580 , 1923 , 24 , 16 , 0 , 42.0 , 4 , 1.2000 ,

2015-03-15 03:00:25 , 1228.1 , 1752.8 , 52.0 , 77 , 2580 , 1923 , 12 , 8 , 0 , 41.7 , 4 , 1.2000 ,

2015-03-15 03:00:26 , 1228.1 , 1752.8 , 52.0 , 77 , 2610 , 1923 , 16 , 10 , 0 , 40.2 , 4 , 1.2000 ,

2015-03-15 03:00:27 , 1228.1 , 1752.8 , 52.0 , 77 , 2580 , 1922 , 26 , 17 , 0 , 44.7 , 4 , 1.2000 ,

2015-03-15 03:00:28 , 1228.1 , 1752.8 , 59.0 , 77 , 2550 , 1918 , 91 , 52 , 0 , 82.6 , 4 , 1.2000 ,

2015-03-15 03:00:29 , 1228.1 , 1752.8 , 62.0 , 77 , 2580 , 1914 , 99 , 58 , 0 , 89.1 , 4 , 1.2000 ,

2015-03-15 03:00:30 , 1228.1 , 1752.8 , 63.0 , 86 , 2550 , 1911 , 99 , 58 , 0 , 89.1 , 4 , 1.2000 ,