97 ram transmission wont engage sometimes

4 wheel drive, shifter moves but tranny doesnt engage sometimes, it doesnty slip or anything out of the ordinary. was wonderin if yall had any tips for me to look at.

Some Mopar transmissions have torque converters that leak down overnight. Because they fill only in gear(real slow) and in neutral.
I used to start the engine then put the gearshift in neutral until the engine oil pressure gauge showed good pressure, after about 3 seconds, then drive away in my '92 W250. Drove it like that for 4 years without any problem.

the engine oil pressure is not the transmission oil pressure though! :(