If I remember, you have to add the IP address that squid listens on to the External cache Managers field in Services - Squid Proxy Server - Local cache.  Your output should look like this:
[2.2.5-RELEASE][admin@pfsense.kominc.local]/root: squidclient -h 10.10.4.1 -p 3128 mgr:info
Sending HTTP request ... done.
HTTP/1.1 200 OK
Server: squid
Mime-Version: 1.0
Date: Wed, 10 Feb 2016 14:49:20 GMT
Content-Type: text/plain
Expires: Wed, 10 Feb 2016 14:49:20 GMT
Last-Modified: Wed, 10 Feb 2016 14:49:20 GMT
X-Cache: MISS from localhost
X-Cache-Lookup: MISS from localhost:3128
Connection: close
Squid Object Cache: Version 3.4.10
Build Info:
Start Time:     Fri, 25 Dec 2015 17:55:34 GMT
Current Time:   Wed, 10 Feb 2016 14:49:20 GMT
Connection information for squid:
        Number of clients accessing cache:      58
        Number of HTTP requests received:       9997622
        Number of ICP messages received:        0
        Number of ICP messages sent:    0
        Number of queued ICP replies:   0
        Number of HTCP messages received:       0
        Number of HTCP messages sent:   0
        Request failure ratio:   0.00
        Average HTTP requests per minute since start:   148.1
        Average ICP messages per minute since start:    0.0
        Select loop called: 261284164 times, 15.499 ms avg
Cache information for squid:
        Hits as % of all requests:      5min: 1.2%, 60min: 3.7%
        Hits as % of bytes sent:        5min: 2.0%, 60min: 0.9%
        Memory hits as % of hit requests:       5min: 9.1%, 60min: 5.6%
        Disk hits as % of hit requests: 5min: 9.1%, 60min: 6.5%
        Storage Swap size:      9437124 KB
        Storage Swap capacity:  90.0% used, 10.0% free
        Storage Mem size:       8100 KB
        Storage Mem capacity:   98.9% used,  1.1% free
        Mean Object Size:       34.64 KB
        Requests given to unlinkd:      0
Median Service Times (seconds)  5 min    60 min:
        HTTP Requests (All):   0.06640  0.06640
        Cache Misses:          0.06640  0.06640
        Cache Hits:            0.00000  0.00091
        Near Hits:             0.00179  0.01164
        Not-Modified Replies:  0.00000  0.00000
        DNS Lookups:           0.03223  0.03374
        ICP Queries:           0.00000  0.00000
Resource usage for squid:
        UP Time:        4049625.975 seconds
        CPU Time:       17684.284 seconds
        CPU Usage:      0.44%
        CPU Usage, 5 minute avg:        0.94%
        CPU Usage, 60 minute avg:       0.80%
        Maximum Resident Size: 478176 KB
        Page faults with physical i/o: 168
Memory accounted for:
        Total accounted:        52310 KB
        memPoolAlloc calls: 1936117391
        memPoolFree calls:  1943865739
File descriptor usage for squid:
        Maximum number of file descriptors:   57960
        Largest file desc currently in use:    267
        Number of file desc currently in use:  135
        Files queued for open:                   0
        Available number of file descriptors: 57825
        Reserved number of file descriptors:   100
        Store Disk files open:                   0
Internal Data Structures:
        272539 StoreEntries
          1887 StoreEntries with MemObjects
          1831 Hot Object Cache Items
        272431 on-disk objects