Question: dsolve,numeric takes more than 12 hours

hi, i have solved my equations with dslove numeric,with 3 terms approximations,it takes maybe 5 minutes to solve it,when i increase 3 terms to 4,it takes more than a day to solve,however my queation is about another problem,
i solved my equations with 3 terms approximation (in 5 minutes),when i want to get answers , for the very little times (i,g=0.00001) it answer quickly,but now i am calculating it for  t=1 seconds and it takes more than 12 hours to answer and it is now continuing calculation for it,which has solved the equations in 5 there any problem?which i can not see?
thnx for your hekp and support 

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