Network suitalble for integrating tensorRT with tensorflow(TFTRT) optimiztion

I‘m work with TFTRT for tensorflow speed-up on GPU. it works well in some classification networks, such as resnet50V2, inceptionV2,VGG19. However, when I try to accelerate the obeject dectetion network like SSD, faster rcnn and mask rcnn, the INT8 networks processed by TFTRT do not gain any advantages in speed over the original network. I doubt that the TFTRT do not favor obeject dectetion network well. And I have two additional questions. Is there some limitaions of the TFTRT? Is there difference in performing INT8 optimzation between tensorRT and TFTRT ?