You may be given a HUB 4 if your area has been upgraded and the network is congested. However if GIG 1 is not available in your area chances are you won't get one. You should not need a HUB 4 although it would be a benefit to ask if your area has them available as they do have a bit of extra power. Would you be able to go to your hubs status page at 192.168.0.1 and in modem mode 192.168.100.1 (unless it is different) copy and paste the router stats the confidential IP's will be removed automatically when you press post. You may be required to log in using your password or the default on the bottom of the hub.
Thanks for your post and sorry to hear that you're getting poorer speeds since your upgrade.
Just to know how we can help further, could you confirm if these speeds were recorded via ethernet connection? Also, are you also experiencing the same speed issues when you take your Hub 3 out of modem mode?
Also, I'd suggest following the advice given by RR-IT-GUY and post your hub stats here so we have a better idea of what's going on and can advise you best.