Market problem over Wifi

[lsiden]

I'm not sure if this is the appropriate place to post this question because this may be a Google Play/Market problem, but here goes:

I've been through several ROMs: Sprint Stock, CM 7.1, Salvage Mod, and now MIUI. Except in stock, I get the dreaded "Package file invalid" when attempting to update large packages over WiFi. It always works when I update over my Sprint phone connection (3G).

There are several things I can rule out that have affected other people:

1. "Allow updates from other sources" is enabled.
2. Allow USB debug mode is enabled.
3. I reset my home WiFi router to get DNS addresses automatically from ISP instead of Google's DNS servers (which I had before).
4. My /cache partition has 160 M, most of which is free, and it got wiped by the new install of MIUI. Besides, if this were a lack-of-disk-space problem, my updates wouldn't work over the phone, but they do work over the phone.

So I'm still at quite a loss why I can't update large apps over my WiFi connection. For example, I just successfully updated the Google Maps app (6.78 M) over Wifi, but get "Package File Invalid" when I try to update Gmail (2.67 M) over Wifi. It works every time over Sprint 3G network.
I've done lots of searching and other people have had this problem, but no one seems to have the fix that works in my case, so I'm going to try my luck in this forum. Thanks for bearing with me!
FWIW - Phone is HTC Evo 4g running Android 4.0.4, kernel version 2.6.38.8-cayniarb-ics-stock-031012+cayniarb@prime #1 PREEMPT Mar 10, Build # MIUI-206150 MIUI