WiMax sites that are really slow most likely have their carriers overburdened. Since Clearwire made the decision to go with LTE, they probably are not adding additional carriers at WiMax sites and just keeping them as is. You can call and complain, and it may help. Clearwire probably does have some additional carrier adds in it's contract with Ericsson, so your complaints may actually cause a ticket to be placed and a carrier added. However, if the problem is pretty uniform across the market, I doubt that Clearwire will add carriers all over.
It may slowly improve as people upgrade their WiMax devices for LTE devices. Every month from here forward there will be less and less WiMax customers until it is shut down in 2015.
The congestion that WiMax is receiving is in no way related to how the LTE network will perform. The LTE network is a ten year network, and WiMax is a dying network. Sprint and Clearwire have incentives to burn cash on their LTE networks, but not on WiMax. WiMax would still be running fine if Clearwire could spend the money for additional carriers (and possibly backhaul). Also, WiMax has a mature device ecosphere, with millions of devices out there. LTE will take years to build the same amount. Also, remember that Sprint shares WiMax with millions of Clear residential and business ISP customers who really suck down the bandwidth (more than 10x's the amount of smartphone users). This will not occur on Sprint's LTE network. The differences are night and day.
Robert