@anderson83
(0734 indicates "Incorrect Gear Ratio 4th. Gear". This would mean slippage is detected between the transmission shafts which are normally "locked together" in 4th. gear. No Bands are applied in 4th. gear, thus rule out Band trouble. In "D" with OD ON (switch not depresssed on shift lever), 4th gear calls for Forward Clutch and Direct Clutch both ON. Either may be slipping. In "D" with OD OFF, all three clutches, including the third, the Coast Clutch are ON. Thus check 4th. gear with both OD ON and OD OFF. Watch tachometer to determine when shifting brings in 4th. gear. First visible rpm drop is 1 to 2, second 2 to 3, 3rd. would be entering 4th. gear. If tach. speeds up, slippage is occurring. If 4th. gear feels normal with OD OFF, Coast Clutch is OK. One of the others is slipping.
If 5th. gear is also slipping, possible OD Band trouble, in addition to clutch slippage. Forward and Direct Clutches are also both engaged in 5th. gear.
Disassembly is needed. imp