I think I may have found the issue. You have the "MinPitch=" and "MaxPitch=" set to the same value in order to fix the missile's angle in the launcher. That works under the [WeaponSystem] entry. However when you are using the SystemType=GUNNER for missiles, even ground attack missiles, you need to set MinPitch=0 so that the gunner can see targets at sea level.
GK-AlSanbouk-TNC-45_mod1_DATA.INI
[Launcher_Base01]
SystemType=GUNNER
GunnerID=5
TargetType=GROUND
MissileRange=72000.0
MinMissileRange=1500
PitchLimited=TRUE
PitchAngleRate=45
MinPitch=12.85 <----------------------------------Change this to 0.0
MaxPitch=12.85
DefaultPitchAngle=12.85
YawLimited=TRUE
YawAngleRate=90
MinYaw=210
MaxYaw=330
DefaultYawAngle=-80
YawModelNodeName=ASMdummy01
PitchModelNodeName=ASMdummy01
MissileLaunchTime=5.0
ViewportPosition=0.387924,-8.15175,3.85665
IndependentSearchChance=100
LookAroundChance=100
GunnerFireChance=100
GunnerFireTime=1.0
MaxMissilesInAir=1