Don't have time this morning, but here is some info from an earlier post. It sums up the situation pretty good.
Generally you can fix it unloaded or fix it loaded. For unloaded you need to lower the center support. You should use kit 05135709AA that includes the spacer and longer bolts. It lowers the support about one inch. To fix it loaded, you need to change the center support bracket to a shorter one as specified in the TSB.
The thing to do is determine if the truck is driven mostly loaded or unloaded. Then fix the symptom that occurs the most. If you only load it up once in a while, don't worry about it if it only does it loaded.
Some new comments 4/8/2008. Have dealer reference TSB 03-003-04 for the basic info. It still applies through 2008 even if it does not specifically say so. The Mega Cab trucks may require two brackets not listed in the TSB. They are 52853309AC and 52853310AA and are 43mm and 62mm in height respectively. The 1" spacer kit 5135709AA also applies to Mega Cab and will generally fix unloaded launch shudder.