Dennis - sounds like you are nearly there. As you suggest yourself, the transmit modulation may be at fault assuming the basic SSB/antenna is working ok.
It might help if you give us a bit more background info on your setup, i.e. which Pactor
TNC? which antenna
tuner? do you have the radio connection for auto tuning? (makes life a lot easier)
Please also ensure the following:
1)You can make regular reliable voice contact - as suggested above.
2)The antenna tuner is working properly & indicating such.
3)The modulation level is correct or at least showing good level on ICOM display whilst trying to connect.
4)You are using latest version of Airmail v3.4.034 or beta v3.4.055
5)Your Pactor modem has latest v4.0 firmware (this is displayed every time you open terminal window).
6)Maybe most important of all, ensure you are trying to connect on correct freq allowing for propagation & using correct centre freq offset.
If you are unsure about your Airmail configuration, select Tools>Setup Wizard - this will take you through your hardware
configuration, putting in correct values were applicable, & saves a lot of time.
If you have IcePack plug-in to Airmail installed you can bring up the propagation window by pressing F8 key with terminal window open. Note Icepack is packaged with latest versions of Airmail & installs with it - just ensure you enter your location for it to work. Stations will be listed according to distance from your location.