hard to get into 1st gear

Recently my 833OD has become increasingly difficult to get into 1st gear after I've been sitting at a light. Often have to force it, or shift thru the other gears while holding in the clutch and then go to 1st.

Note: it gets worse when it gets hot, stuck in alot of traffic. Even shifting thru all the gears with the clutch in becomes sticky at every gear when it gets hot outside and stuck in traffic.

Is something wearing out? out of adjustment? or just need to try a different fluid? I'm using 90 wt gear oil.

Thanks for your suggestions!