Thermostat ?

When ever I drive my truck for about 10 or so mins all at once the temp. Gauge gets up pretty hot then slowly goes down after that, then it stays normal. Is this my thermostat?

Could be if it's stuck closed (but the temps should still gradually go up) - then get real hot til the t-stat 'pops' open, then that would regulate your temperatures again.

How are your fluid levels? It almost sounds like you are getting a steam bubble or an air pocket. Next time you have 10 mins ... let it idle and feel your upper and lower radiator hoses (while watching the temp gauge). Feel your upper radiator hose....if it gets hot, your thermostat is OPEN. Wait for that temp spike and feel the upper hose. If it's cool, then once the temp gauge gets hot - it get's hot too - then you might have a t-stat that's stuck closed (or too high an opening temp).

If all feels normal and all of a sudden the temp gauge spikes up (and the hoses all feel warm (but not drastically hot all of a sudden), I'd say check your temp sender at the thermostat cover. Just check that connection anyhow - might be loose? Make sure it's on there tight and clean.

Forgot to mention its only when you drive it, but I bought a new thermostat so ill go ahead and change it and see how it does.and my fluids are all good

I just replaced my bad thermostat (truck never warmed up all winter, ha!), and this is how my new thermostat performs. It climbs up to a hair above half way then drops down to a little above the second line within 10 minutes or so of driving then doesn't climb at any point afterwards.

How to make this short.My 87 runs about a 1/4 above cold.Mine used to climb up not half way but then drop back.The real problem was radiator was well old(like 23 yrs) and same for heater core.I did 3 things new water pump(was leaking) new heater core and new radiator.I replaced my upper/lower hoses,new heater core hoses,new intake hoses under intake,new thermostat and new rad cap.I would at least flush your cooling system with some lime away (or like branded product).This will remove years of build up internally and drain,refill with one bottle lime away and water (about 2gallons).Leave your rad cap off,heat on,fan high let idle for 20min.Once water burps over rad fill cap it.Then drain refill with water only let idle 15 min,same process.Then drain.Now your ready for your coolant and USE distilled water(one gallon) and add coolant(I use almost a gallon) to get it to MY choice not 50/50.By placing some cardboard between the rad support and radiator speeds up the heat cycle to get to operating temps.Remove this once you are DONE!!!!Granted this may be way to much info and not your scenario,but I know once I replaced my radiator and heater core the difference in warm up,and or cooling was like well brand new truck.Plus old crappy water pump leaking.Flushing with lime away removes years of trash the prestone and or typicall flushes never remove imo and have pics to prove that.

was my 1st flush after my new radiator,new wp,new heater core.The lime away (off brand name I used from dollar general) that cleared out my block from years of build up.

I'll see how it does when I install my thermostat

Ohhh ... that's a VERY good idea!! I think I need to do that myself. Thanks for the thought!