CPU frequency does not change

The CPU always runs at a constant frequency. The operating speed is determined by a multiplier. You are confusing them. If the CPU multiplier is 3, then the operating speed will be 2.4 GHz - three times the CPU frequency.

Your problem has nothing to do with this unless you have it connected to the wall charger and have removed the battery. In this case the CPU is throttled back by half.

Ways to help make a slow Mac faster

17 Reasons Why Your Mac Runs Slower Than it Should

Slow Mac Performance? This Article Solves It!

Fix slow start-ups in OS X | MacFixIt - CNET Reviews

6 Easy Tips to Speed Up OS X Yosemite on Your Mac

Avoid using any third-party software that claims to clean up your computer. Usually this software does more bad than good. Furthermore, you don't need it. Note that all computers will become slower over time even under normal use. Experienced users typically erase the hard drive and do a clean install from scratch at least once a year or whenever installing a major OS upgrade. Of course doing so also means you must maintain regular and multiple backups.

Add more RAM or cut back on the number of concurrently running applications and utilities. Remove unnecessary software such as anti-malware and software that promises to clean your Mac. Check for runaway processes: Runaway applications can shorten battery runtime, affect performance, and increase heat and fan acti… Also see:

Pre-Mavericks

Open Activity Monitor in the Utilities folder. Select All Processes from the Processes dropdown menu. Click twice on the CPU% column header to display in descending order. If you find a process using a large amount of CPU time (>=70,) then select the process and click on the Quit icon in the toolbar. Click on the Force Quit button to kill the process. See if that helps. Be sure to note the name of the runaway process so you can track down the cause of the problem.

Mavericks and later

Open Activity Monitor in the Utilities folder. Select All Processes from the View menu. Click on the CPU tab in the toolbar. Click twice on the %CPU column header to display in descending order. If you find a process using a large amount of %CPU, then select the process and click on the Quit icon in the toolbar. Click on the Force Quit button to kill the process. See if that helps. Be sure to note the name of the runaway process so you can track down the cause of the problem.

The Ultimate Fix

Backup everything, erase the drive, reinstall OS X, and restore your data from the backup. Reinstall third-party software from original media/scratch.

Then it isn't slow. It can't be both clean and slow as that is contradictory. You can download EtreCheck and run it on your computer. Male a copy of the report and post it here in a reply by pasting it into your reply.

Since it is new you can take advantage of returning it for repair or replacement under your warranty. You can also take advantage of your free 90 day telephone support.