Ive had this Blazer for about 3 or 4 months. since ive had it i have consistently had a problem with it bumping. If i press the gas, after it kicks into first itll feel like its hitting small bumps. and it does it up until it hit 55-60 mph. If i lay on the gas in 1st or 2nd the bumps are extremely rapid, and if i let off the gas itll stop. i would love to have some help troubleshooting this.

 

Sounds like either an engine misfire, or possibly a driveline problem, maybe a failing universal joint. Are there any trouble codes in memory, or is the check engine light on? Have you removed the drive shafts to check for worn/loose u joints?