IP based irule

One thing that may be helpful to at least see what's happening in the iRule would be to add some logging. That will let you know what's actually going on. Is this an HTTP request, or something different (what port is being used)? If HTTP, you should set the pool in HTTP_REQUEST instead or CLIENT_ACCEPTED. Then you can check the ltm logs and see what's happening.

when CLIENT_ACCEPTED {
    log local0. "Client IP: [IP::remote_addr]"
    if { [IP::addr [IP::remote_addr] equals X.X.X.0/25] || [IP::addr [IP::remote_addr] equals Y.Y.Y.0/25]} {
        log local0. "  Setting pool p_pe_01"
        pool p_pe_01
    } elseif { [IP::addr [IP::remote_addr] equals X.X.X.128/25] || [IP::addr [IP::remote_addr] equals Y.Y.Y.128/25]} {
        log local0. "  Setting pool p_pe_02"
        pool p_pe_02
    } else {
        log local0. "  Setting pool p_gw"
        pool p_gw
    }
}