set up new gmail account with importing old emails from current account

I think I can help you with your issue. I also faced issues of importing my contact list from an existing account to my new account but eventually I figured the right way and imported them easily.

Hello, I am skilled unix and network engineer with 5 years of experience in unix based systems, virtualization like proxmox , iptv,zimbra etc. I like to automate system working with additional shell scripts. I have fresh account on this site and have not any comments, but I can help you with this Your task can be solved in few hours with my help. Give me access and I'll do it and can answer all your questions. I have many scripts that are working fine for different tasks. I can sync two accounts for migrating old emails. Best regards, Alex.

I can give to support for step by step importing email from old Gmail account to new Gmail account. Since this needs to sign in your old & new account. so It's better that this should be done by you. I can show you by example how to do with snapshots of each steps.