irule forwarding to gtm address based on port

Well, yes, if the VIP is only configured for port 80, it will ignore any other port traffic. If you need to capture port 9074 requests, then perhaps you need to configure the VIP with a wildcard port and use an iRule to restrict it:

when CLIENT ACCEPTED {
    switch [TCP::local_port] {
        "80" -
        "9074" { return }
        default { drop }
    }
}
when HTTP_REQUEST {
    if { [TCP::local_port] equals "9074" } {
        HTTP::redirect "http:://test.com"
    }
}