Internet speed

Why is it that my high speed internet works fine on everything else and is miserable on my cox email? You have been to my office twice. You replaced my coax, you gave me a new modem, you have checked everything that you thought should be checked. I have used it on multiple computers and have tried fire fox, yahoo, google and outlook. It's always the same story. You showed me where I am getting the speed I should be getting through a phone call and on line and that was great, I am. I have waited as long as 3 minutes for 5 pages to upload. It takes forever just to get on line. I am a realtor and do a lot on the computer. I print as many as 500 sheets a month. and scan half of that. Cox Email is miserable for ME. Shouldn't I have the same speed no matter what I do? For 70.00 a month I feel that my EMAIL Isn't doing the job. It has been going on for a long time and it would be very difficult for me to change.