Actually, the big 3 are trying to mimic the Japanese business plan of having less stock sitting on the lots. This reduces overhead/cost, and leads the buyers to believe they're harder to get, which gives the dealer the upper hand in making a deal.
Chrysler HAD been working on the 180 day stock level - at any time, if the plants shut down, the dealerships had (theoretically) 180 days worth of stock to get them through until the model was being built again. Now, it appears they're more in line with the 60 day plan (which the Japanese used partly because of time to ship overseas, and the US hopes circumvents possible strikes by UAW/CAW). The ideal is supposed to be something like 45 days worth of stock.