Thanks for choosing justanswer.com! Your issue is most likely going to be a plugged radiator. If you put the heater on max heat does the temperature drop? If so this is an indicator the radiator is plugged.
If the temp does not drop (or move) the water pump may have broken impellers causing the coolant to not flow correctly when driving.
Being that it is at drive speeds the fan is not needed as much.
When it starts to get hot, if you touch the upper and lower hose do they feel to be about the same temp or is one cooler than the other?
Being I am not going to be online at this time tomorrow (tuesday - saturday I get online later at night) I will opt out on this question so another tech can assist you and maybe give you a better description on what to check for.
Thanks for coming to Just Answer to ask a question.
Different expert here
Going to need to know the current miles and engine size and what you have done so far?