I've taken several actions to deal with these slow speeds:
1. Perhaps the most important has been to click out of suggested "upgrades" to Sprint Smartview software offered by popups on my screen - in the most recent case while Smartview was not even running! And, the pop-up indicated that I would have to have detailed information about my account, my hardware, and - get this - possibly my driver's license to accomplish the upgrade. NO THANKS!
2. I disabled QOS in Wireless Network Connection Properties.
3. I disabled NetBios over TCP/IP in Advanced TCP/IP Settings of Internet Protocol (TCP/IP) Properties from the Wireless Network Connection Properties window.
4. I installed a CPT500 Wireless broadband router, which handles the connection to the Sierra 598U modem instead of using Smartview for that purpose. This means my laptop does not have to use the Smartview software, lightening the application load. And the Cradlepoint firmware seems to do a better job of interfacing with the Sierra modem anyway - Cradlepoint has been purchased by Sierra, IIRC.
5. I stopped and then disabled the Novatel Wireless "Novacore SDK" Windows XP service which I had not installed and had not been aware was running on my machine, after confirming with the company which built the application that it did not belong on a user machine and that I could safely disable it. No one has been able to tell me why or how this service was installed and running on my machine.
Current speed report is a bit slower than usual these past few days, but acceptable: