I would question the charges, and all 401K plans are required to disclose them annually under IRS rules. Ask your HR department for a copy of the report.
I administer my company's 401K plan and we used to be with Great West. We ditched them after I did a review of the fees. The fees to the employer under the Great West plan and our new plan are about the same. The difference came in within the funds themselves -- all those buried expenses that employees pay that aren't easy to follow and readily apparent. So it's not like the employer is pocketing the savings, it's just that the hidden fees aren't eroding our employees' returns, unbeknownst to them.
Great West had higher record-keeping, investment management, and trustee fees that were mostly buried in the funds and costing our employees an extra $15K per year. This is borne out by the expense ratios of the various funds, which were markedly lower. Under the new arrangement we also became a participant in a large group plan (through a professional association) and gained access to more funds, and institutional classes of funds.
I don't know what size employer you work for, but our group was small (less than 25 participants). By joining with a large group plan (offered through a professional association) we gained access to more options and oversight from a board. I have more confidence in that sort of group to make decisions about plan offerings than a locally controlled panel -- which often consisted of me, our manager, and a representative from Great West.
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