GenotypeSummaries

Hi GATK team,
I have a multi-sample vcf file of WES patient samples created by HaplotypeCaller. After applying VQSR, and DP filter, I have got TiTv ratio of 2.59, which is a bit low and should be near 3.0 for whole exome data. I am considering filter vcf file further based on GQ field. How can I perform filtering based on GQ, because in the vcf file, there are 5 GQ values, one each for each sample. I noted a walker GenotypeSummaries which adds annotation GQ_mean to the INFO field, but perhaps is not available for GATK v.3.7. I need suggestion to improve TiTv ratio, or how to filter the vcf file based on average/commulative GQ.
Thanks