05 Nissan quest S 3.5

Im jw if anyone could give me what my most likely problems could be with my Nissan quest 3.5
van idk if it would have anything to do with what im trying to figure out but my rpm meter
completely stopped working and i had to replace the alternator about a week ago but this was
happening b4 and after  i changed the alternator but anyways first after the van has been sitting
for 6to12 hours it cranks way longer than normal be4 it will start but once its been running i can
turn it over and it starts normal not sure if this could help in figure out the problem but i am
hoping so also seems like it has a slight miss when first started  but after its running seem to
run and idling till i have to drive between 45AND55 mph then it seems to start missing or kinda
jerking but if i give it just a little more gas than needed to run this speed  then it straightens out
but it definitely seems like when i have to run around 45 50 mph and i cant gove it more gas i
have to let off the gas but its hard to stay at the speed i need to be and stop the jerking and it
definitely cause it to get worse gas mileage and suggestions that could keep me from spending
money i don't have to would be very appreciated ty