You will not be able to find a definitive answer on whether you will be allowed back into the US, as it will depend on the exact circumstances, and the feeling of the immigration officer when you re-enter.
As your existing I-94 will expire whilst you are in Mexico, your re-entry will be treated as a new trip to the US. The amount of time you spent in Mexico will not be counted against your previous entry to the US - although it's likely you'll be asked to show proof of when you did leave the US so they can consider how long you were in the US on your previous entry.
The issue thus becomes one of re-entering the US after a previous extended stay. Based on what you've described, you'll have been in the US for at least 4.5 months, out for country for around 1.5 months, and are now looking to re-enter the US.
There is no formalized rule for how long you must stay out of the US between trips, however the border staff will want to have some indication that you are actually a bona fide tourist, and not "living" in the US. The general guideline they use for determining this is that you must spend as much time out of the US as you spent in it. Given you have spent much more time in the US than outside of it, it is very likely you will have issues when trying to re-enter.
If you are able to show plans to leave the US after a period of time (eg, airline tickets departing a month or so after you enter the US) then you will likely be admitted without issue. If instead you have no plans to leave, and thus the CBP staff believe you are attempting to reside in the US, then you may find that you are admitted with only a short stay allowed (ie, not the full 180 days you are expecting), or even not admitted at all.
However as I said above, this is all conjecture based on the vague facts you've provided. It's possible you'll be admitted for another 6 months without issue - however I would not consider that likely given what you've described.
