General Motors and Ford, both reeling from lower-than-expected June sales, have decided to extend their 4th of July sales through the rest of July. While extending rebates and incentives is not uncommon practice, in this case the extensions are a result of Toyota's heavily stepped up Tundra incentive program.

Toyota caught Ford and especially GM off guard when it introduced hefty incentives on the brand new Tundra pickup. GM's equally new Silverado and Sierra trucks didn't match Toyota's rebates and the sales figures showed it.

Toyota had about $5,000 worth of incentives on average on its Tundras last month, whereas GM offered merely $3,600 on average. Thus, Toyota's sales jumped 146 percent over 2006's Tundra sales and GM's dropped 20 percent.

Actual incentives vary by region, but GM is adding an additional $1,000 "bonus cash" on all of its trucks as it tries to gain back lost market share.