If you get proper range with a Futaba receiver when you use your Futaba transmitter, then you'll need to check to see what may be wrong with your receiver. Remove the equipment from the airplane and do a range check with the receiver supported above the ground with the receiver antenna extended vertially (don't use a metal support). See what range you get then.

No way for us to tell you what may actually be wrong. If you get normal range with a Futaba receiver, then it's not your transmitter. If you don't, then your transmitter may require service or repair.