E-mail problems from an InMotion hosting account with valid DKIM and SPF records and corporate Gmail clients

Hi folks. I'm reasonably experienced with e-mail and DNS records. The cPanel-based diagnostic under "eMail Deliverability" in my InMotion Hosting indicate that my SPF and DKIM records are valid.  I've checked external web tools for sender reputation as well. All seem to indicate that my sender reputation is fine as are the InMotion servers. 99%+ of my e-mail works perfectly. I have two corporate customers that I constantly have issues exchanging e-mail with however. Sometimes I don't receive their e-mail - other times they don't receive mine. Neither of us receive non-delivery notifications. I'm embarrassed - they naturally assume that I'm the problem because I have the smaller company. I've never had a problem with anyone else other than these two domains - I'm turned off the InMotion Spam Assassin SPAM filter.  I'm not 100% sure, but I believe that both of these customers use Gmail for company e-mail. I'm just wondering whether anyone else in the InMotion community is having similar problems with corporate Gmail customers - I recall a customer that I dealt with previously telling me that Gmail provided the ability to suppress non-delivery (which I see as a bad idea of course) . I suspect this is not an issue with InMotion Hosting, but it's causing me a lot of grief. I'm working around this now by sending from a separate account I have hosted @ GoDaddy which seems to work for whatever reason. Wondering if anyone else has come across something similar? Thanks very much.