I'd have to have more information to go on. But on just a guess I'd say it has to do with the shift range of the transmission. 1st to 2nd would require a certain speed or r.p.m. range, before it shifts from 1st to 2nd gear. Or vice versa (down shift). Certain transmissions can be programed to shift from, 1st gear to 3rd or 4th gear automatically. Just by how hard your on the gas.Automatic transmissions work by pressure and heat.The vehicles engine produces a vacuum.The higher the heat and r.p.m.'s the more pressure is forced by the vacuum.The transmission then shifts. Alot of new model vehicles tend to have "rev out" .The transmission will carry the gear into higher r.p.m.'s. Before the computer allows the transmission to make the shift.Based on how hard your on the gas.